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1706
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1 *
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2 * GIF supervisor and LZW decoding stuff.
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3 *
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4
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5 ifp1
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6 use /dd/defs/os9defs.a
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7 endc
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8
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9 psect view_gif_a,0,0,0,0,0
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10
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11 *
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12 * GIFshowpic
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13 *
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14 * Display a GIF picture
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15 *
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16 vsect dp
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17 * These are initialized by SetGIF in view_gifset.a
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18 giftable: rmb 2 Pointer to 12k decode table
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19 gifstack: rmb 2 Pointer to 4k space for reversing codes
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20 * These are used by the actual screen output routines in view_gifpix.a
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21 gifiheight: rmb 2 Image height
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22 gifiwidth: rmb 2 image width
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23 gifinterlace: rmb 1 T=Use interlace in displaying picture.
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24 * These are all used locally.
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25 sheight rmb 2 Screen height (We use the image size instead of these).
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26 swidth rmb 2 Screen width
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27 domap rmb 1 T= Color map follows
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28 *cr rmb 1 Number bits of color resolution
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29 pixel rmb 1 Number bits per pixel
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30 background rmb 1 Background color
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31 screenset rmb 1 T= screen has been set.
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32 endsect
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33
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34 GIFshowpic:
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35 clr screenset
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36 lbsr signature Find signature in input stream
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37 lbsr screendesc Parse the screen descriptor information
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38 tst <domap
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39 beq noglobal
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40 lbsr colormap Read and parse the colormap and set up the screen.
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41 clr <domap
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42 noglobal
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43 *
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44 * Main image processing loop
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45 * Searches the input stream for one of the following separator characters,
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46 * and acts accordingly:
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47 * 0x2c (comma) - GIF image follows
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48 * 0x21 (exclamation point) - extension block follows
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49 * 0x3b (semicolon) - end of GIF file
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50 GIFLoop
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51 lbsr I_GetByte
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52 lbcs _error
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53 cmpa #$3b semicolon marks the end of the file
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54 beq GIFend
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55 cmpa #$21
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56 bne gif2
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57 lbsr skipextension
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58 bra GIFLoop
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59 gif2
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60 cmpa #$2c
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61 bne GIFLoop
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62 bsr gifimage
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63 bra GIFLoop
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64 GIFend
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65 lbsr EndGIF Return extra memory area.
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66 rts
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67
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68 vsect dp
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69 mincode rmb 1 Starting code size
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70 lastcode rmb 2 Last code input
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71 thiscode rmb 2 the current code
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72 endcode rmb 2 Code signifying end of picture
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73 clrcode rmb 2 code indicating that we clear the table
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74 firstcolor rmb 1 First color of code just processed
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75 codesize rmb 1 Current code size in bits
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76 *bethy rmb 50 How much I love Beth. (Needs to be MUCH bigger...)
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77 endsect
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78
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79 * Process a GIF image
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80 gifimage
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81 pshs a,b,x,y,u
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82 * First, handle the image descriptor
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83 lbsr GIFgetword offset of pic from left edge of screen
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84 lbsr GIFgetword offset of pic from top of screen
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85 lbsr GIFgetword image width
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86 std gifiwidth
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87 lbsr GIFgetword image height
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88 std gifiheight
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89 lbsr I_GetByte bitmapped option byte
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90 tfr a,b
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91 sex
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92 sta domap top bit: T=local map follows
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93 tfr b,a
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94 anda #$3
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95 inca
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96 sta pixel Bottom 3 bits: bits/pixel less one.
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97 lslb
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98 sex
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99 sta gifinterlace Bit 6: T=Use interlace
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100 tst domap Is there a local color map?
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101 beq nolocal
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102 lbsr colormap Yes, handle it.
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103 nolocal
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104 * Now, we're down to the actual image.
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105 lbsr I_GetByte Get the starting code size.
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106 sta mincode
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107 cmpa #8 Does code size make sense?
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108 bls gifcodeok
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109 lbra E$Format No, report a format error.
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110 gifcodeok
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111 lbsr lzwinit Initialize some machinery
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112 lbsr gifoutinit
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113 * From here on, U holds the address of the next entry in the decode table.
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114 lbsr clrtable Clear table, set endcode and clrcode
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115 imageloop
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116 lbsr nexttoken Get a code.
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117 stx thiscode
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118 cmpx endcode Is it an end-of-pic code?
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119 beq imageend
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120 cmpx clrcode Is it a clear code?
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121 bne imagenormal
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122 lbsr clrtable If so, reinitialize everything.
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123 lbsr nexttoken Get the next token (always a root)
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124 stx lastcode
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125 lbsr outcode Output it.
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126 bra imageloop
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127 imagenormal
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128 lbsr outcode Output the code, set the initial color var.
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129 ldx lastcode
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130 lda firstcolor
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131 stx ,u++ Add the code to the decode table.
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132 sta ,u+
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133 cmpu <codelimit Are we at the point where we change code size?
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134 blo addcend
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135 lbsr setlimit Yes, do it.
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136 addcend
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137 ldx thiscode
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138 stx lastcode
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139 bra imageloop
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140 imageend
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141 puls a,b,x,y,u,pc
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142
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143 * This is an extension block, so skip it.
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144 skipextension
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145 pshs a,b,x,y
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146 lbsr I_GetByte Get function code
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147 extensloop
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148 bsr getpacket Get packet, size in A.
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149 tsta
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150 bne extensloop Non-zero, get another.
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151 puls a,b,x,y,pc
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152
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153 * Get a packet from input into AltBuff, return packet size in A.
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154 getpacket
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155 pshs b,x,y
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156 lbsr I_GetByte
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157 tsta
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158 beq getpackend
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159 pshs a
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160 tfr a,b
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161 clra
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162 leax altbuff,y
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163 tfr d,y
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164 lbsr I_Read
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165 lbcs _error
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166 puls a
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167 getpackend
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168 puls b,x,y,pc
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169
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170 * Read and process colormap
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171 colormap
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172 pshs a,b,x,y,u
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173 lda pixel
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174 bsr powertwo
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175 leax altbuff,y
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176 leau alt2buff,y
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177 pshs y
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178 tfr d,y
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179 leay d,y
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180 leay d,y Y:=3*D
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181 lbsr I_Read Read global color map
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182 lbcs _error
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183 puls y
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184 tst <screenset Is screen already set?
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185 bne endcmap Yes, don't process stuff.
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186 com screenset No, mark it as set.
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187 lbsr GIFcolors Translate colors, and generate color translation table.
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188 lbsr setscreen
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189 lbsr setbuffer
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190 lbsr setpals Set the palettes
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191 lda background Translate background color through the translation table
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192 leau a,u
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193 leau a,u
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194 lda a,u
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195 lbsr setborder Set the border color.
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196 endcmap
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197 puls a,b,x,y,u,pc
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198
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199 * Take value in A and return 2**A in D (assumes A<15).
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200 powertwo
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201 pshs a
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202 ldd #1
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203 tst ,s
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204 powerloop
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205 beq powerend
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206 lslb
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207 rola
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208 dec ,s
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209 bra powerloop
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210 powerend
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211 leas 1,s
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212 rts
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213
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214 * Read and process screen descriptor
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215 screendesc
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216 pshs a,b
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217 bsr GIFgetword
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218 std swidth First word is screen width in pixels
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219 bsr GIFgetword
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220 std sheight Next is screen height in pixels
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221 lbsr I_GetByte This is bit-mapped
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222 lbcs _error Bit 7: T= global map follows
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223 tfr a,b Bits 6:5:4: number bits of "color resolution" - 1
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224 andb #7 Bits 2:1:0: Number of bits per pixel - 1
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225 incb (Determines size of color map)
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226 stb pixel
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227 tfr a,b
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228 sex
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229 sta domap Top bit is true if global color map follows
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230 lbsr I_GetByte
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231 lbcs _error
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232 sta background
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233 lbsr I_GetByte
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234 lbcs _error
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235 tsta
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236 lbne E$Format
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237 puls a,b,pc
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238
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239 GIFgetword
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240 lbsr I_GetByte
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241 lbcs _error
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242 tfr a,b
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243 lbsr I_GetByte
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244 lbcs _error
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245 rts
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246
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247 * Signature: scan input to find "GIF###", the GIF signature string,
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248 * where ### is two digits followed by a lowercase letter, e.g.
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249 * '87a'
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250 sigsub
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251 lbsr I_GetByte
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252 lbcs _error
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253 rts
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254
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255 signature
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256 pshs a,b
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257 Sig0
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258 bsr sigsub
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259 Sig1
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260 cmpa #'G Search for "GIF"
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261 bne Sig0
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262 bsr sigsub
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263 cmpa #'I
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264 bne Sig1
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265 bsr sigsub
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266 cmpa #'F
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267 bne Sig1
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268 clrb
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269 Sig2
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270 bsr sigsub Get two digits
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271 cmpa #'0
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272 blo Sig1
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273 cmpa #'9
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274 bhi Sig1
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275 comb
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276 bne Sig2
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277 bsr sigsub and one lowercase letter
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278 cmpa #'a
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279 blo Sig1
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280 cmpa #'z
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281 bhi Sig1
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282 puls a,b,pc
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283
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284
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285 *
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286 *LZW decode subs.
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287 *
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288 vsect dp
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289 codelimit rmb 2 Point at which we must switch code sizes.
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290 endsect
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291
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292 * Miscellaneous initialization
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293 lzwinit
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294 pshs a,b,x
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295 clr <packsiz
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296 clr <numbits
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297 puls a,b,x,pc
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298
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299 * Initialize the decode table
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300 *
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301 clrtable
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302 pshs a,b,x,y
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303 ldx giftable Get start of table
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304 lda mincode
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305 lbsr powertwo
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306 pshs y
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307 tfr d,y
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308 clra
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309 clrb
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310 clrloop
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311 sta ,x+ Roots have 0 for pointer, themselves for suffix
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312 std ,x++
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313 incb
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314 leay -1,y
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315 bne clrloop
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316 puls y
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317 stx clrcode
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318 leax 3,x
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319 stx endcode
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320 leax 3,x
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321 tfr x,u Set up nextentry pointer in U
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322 lda mincode
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323 sta codesize Pretend we were doing "mincode".
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324 lbsr setlimit Bump to next codesize.
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325 puls a,b,x,y,pc
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326
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327 vsect dp
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328 packptr rmb 2
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329 packsiz rmb 1
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330 endsect
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331 * Return next byte from file
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332 nextbyte
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333 pshs x
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334 tst packsiz
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335 bne nextbyte1
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336 lbsr getpacket
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337 sta packsiz
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338 leax altbuff,y
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339 stx packptr
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340 nextbyte1
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341 dec packsiz
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342 ldx packptr
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343 lda ,x+
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344 stx packptr
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345 puls x,pc
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346
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347 vsect dp
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348 numbits rmb 1 Number of bits in bit buffer
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349 bitbuff rmb 3 Buffer bits from file here
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350 codemask rmb 2 Mask off just codesize bits.
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351 endsect
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352 * Return next token from file
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353 nexttoken
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354 pshs d
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355 ldb numbits First, fill bitbuffer with enough bits to make up codesize
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356 bra nexttokst
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357 nexttokloop
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358 ldx bitbuff Move other 16 bits forward.
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359 stx bitbuff+1
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360 bsr nextbyte Get 8 more bits
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361 sta bitbuff
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362 addb #8 Increase bit count.
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363 nexttokst
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364 cmpb codesize
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365 blo nexttokloop
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366 stb numbits
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367 cmpb #17 Do we have to deal with three bytes?
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368 blo nexttok2 No, 16 or fewer bits, so just deal with two.
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369 ldb #20
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370 subb numbits First, we shift until we get to bit #20.
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371 clra
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372 tfr d,x
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373 ldd bitbuff We keep first two bytes in D, leave 3rd one in place.
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374 nexttok31
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375 lsra Analysis shows that we are never past bit 19, so we will
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376 rorb always have to process this loop at least once.
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377 ror bitbuff+2
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378 leax -1,x
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379 bne nexttok31
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380 tfr b,a Now, the first bit of the token we want is out of the first
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381 ldb bitbuff+2 byte, so we're down to two bytes.
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382 lsra
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383 rorb Since we start with the least sig bit in bit #20, and we want it
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384 lsra in bit #24, we must shift exactly 4 times.
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385 rorb
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386 lsra
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387 rorb
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388 lsra
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389 rorb
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390 bra nexttok10 Now we have our token.
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391 nexttok2
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392 cmpb #9 Do we have to deal with two bytes?
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393 blo nexttok1
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394 ldb #16
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395 subb numbits
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396 clra
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397 tfr d,x
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398 ldd bitbuff
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399 stx -2,s Test X for zero.
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400 beq nexttok10
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401 nexttok21
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402 lsra
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403 rorb
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404 leax -1,x
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405 bne nexttok21
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406 bra nexttok10
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407 nexttok1
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408 ldb bitbuff
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409 lda #8
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410 suba numbits
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411 beq nexttok10
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412 nexttok11
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413 lsrb
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414 deca
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415 bne nexttok11
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416 nexttok10
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417 anda codemask
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418 andb codemask+1
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419 ldx <giftable
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420 leax d,x
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421 leax d,x
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422 leax d,x
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423 ldb numbits
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424 subb codesize
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425 stb numbits
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426 puls d,pc
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427
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428 outcode
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429 pshs a,b,x,y,u
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430 ldu <gifstack
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431 cmpx 6,s U is on the stack.
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432 lbhi E$Format If the code is too large, report a format error
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433 beq outcode1
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434 bsr outcsub If it's in the table, process it.
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435 bra outcode2
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436 outcode1
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437 ldx lastcode If it's not in the table, then it is the last code
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438 bsr outcsub followed by the first color of the last code.
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439 lda firstcolor
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440 lbsr gifoutpix
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441 outcode2
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442 puls a,b,x,y,u,pc
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443
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444 outcsub
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445 pshs y
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446 ldy #0000
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447 outc1
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448 lda 2,x
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449 leay 1,y
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450 pshu a
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451 ldx ,x
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452 bne outc1
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453 tfr y,x Put the count in X
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454 puls y
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455
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456 sta firstcolor Now we know the first color, so store it.
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457
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458 outc2
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459 pulu a
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460 lbsr gifoutpix
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461 leax -1,x
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462 bne outc2
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463 rts
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464
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465 * Add a code to the table
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466 addcode
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467 pshs a,b
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468 puls a,b,pc
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469
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470 setlimit
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471 pshs a,b,x
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472 lda codesize
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473 cmpa #12
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474 bhs setlim1
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475 inca
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476 setlim1
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477 sta codesize
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478 lbsr powertwo
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479 ldx giftable
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480 leax d,x
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481 leax d,x
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482 leax d,x
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483 stx codelimit
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484 subd #1
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485 std <codemask
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486 puls a,b,x,pc
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487
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488 endsect
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