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1706
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1 *
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2 * Setup and Screen support for GIF
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3 *
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4 * Globals
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5 * gifoutinit -- Initialize output machinery
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6 * gifoutpix -- output one pixel, with scaling, etc.
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7 *
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8 ifp1
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1912
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9 use os9defs.d
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1706
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10 endc
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11
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12 psect view_gifpix_a,0,0,0,0,0
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13
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14 *
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15 * Screen support-- output one GIF pixel to screen, with scaling and dithering.
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16 *
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17 vsect dp
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18 pixpline rmb 2 Number of pixels on a virtual screen line.
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19 pixscrn rmb 2 Number of pixels on actual screen line.
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20 pixcnt rmb 2 Count of pixels on actual screen line.
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21 lineptr rmb 2 Pointer to linebuff, for putting pixels
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22 pixleft rmb 2 Number of pixels left for this GIF line
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23 horscale rmb 2 Horizontal scaling counter.
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24 linecount rmb 2 Current GIF line number
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25 linenumb rmb 2 Current Coco Line number
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26 linemax rmb 2 Max Coco line number
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27 lineinc rmb 2 Increment between lines
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28 verscale rmb 2 vertical scaling counter.
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29 endsect
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30
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31 * gifinterlace holds T if we do interlace.
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32 gifoutinit:
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33 pshs d,x
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34 ldd #1
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35 tst <gifinterlace
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36 beq init1
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37 ldd #8
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38 init1
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39 std lineinc
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40
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41 ldd #0
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42 std linecount
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43 std horscale
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44 std verscale
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45
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46 ldd <Skipcols
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47 bpl init20 Default value is zero
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48 ldd #0
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49 std <Skipcols
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50 init20
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51
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52 ldd <Skiplines
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53 bpl init21 Default value is zero
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54 ldd #0
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55 std <Skiplines
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56 init21
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57
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58 ldd #0
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59 subd <Skipcols
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60 std pixcnt
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61
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62 leax linebuff,y
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63 stx lineptr
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64 ldd <gifiwidth
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65 std pixleft
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66
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67 ldx #320 Type 8 and 6 screens are 320 pixels across.
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68 lda <type
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69 cmpa #8
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70 beq init8
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71 cmpa #6
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72 beq init8
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73 ldx #640 Type 7 and 5 are 640 pixels across.
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74 init8
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75 stx pixscrn
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76 stx pixpline
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77
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78 ldd #192 For default size, scale pic to 192 lines.
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79 std linemax
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80
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81 lda <Size
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82 bne init98
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83 ldx <gifiheight For small, choose divisor of actual height.
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84 clra
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85 pshs a
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86 init92
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87 inc ,s
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88 lda ,s
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89 lbsr div168 Divide height by number
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90 cmpd #200
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91 bhi init92 If not <200, keep going
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92 std linemax
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93 puls a Clear stack
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94 bra init99
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95 init98
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96 cmpa #2
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97 bne init99
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98 ldd <gifiheight Huge is 1:1 height
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99 std linemax
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100 ldd <gifiwidth And 1:1 width
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101 cmpd <pixscrn ... but not less than screen width
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102 blo init99
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103 std pixpline
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104 init99
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105
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106 puls d,x,pc
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107
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108 * Output pixel to screen
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109 *
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110 * Expects
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111 * alt2buff holds color translation table
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112 * A holds pixel to output
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113 * gifiheight, gifiwidth hold picture dimensions
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114 gifoutpix:
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115 pshs a,b,x
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116 tst verscale
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117 bmi outpix5
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118 ldx lineptr
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119 ldd horscale
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120 subd pixpline
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121 std horscale
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122 bpl outpix5
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123 outpix1
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124 ldd pixcnt
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125 addd #1
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126 std pixcnt
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127 bmi outpix11
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128 cmpd pixscrn
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129 bgt outpix11
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130 lda ,s
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131 sta ,x+
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132 outpix11
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133 ldd horscale
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134 addd <gifiwidth
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135 std horscale
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136 bmi outpix1
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137 stx lineptr
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138 outpix5
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139 ldx pixleft Count down number of GIF pixels on this line.
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140 leax -1,x
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141 stx pixleft
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142 bne outpix9
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143 tst verscale
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144 bmi outpix7
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145 lbsr dithline Translate GIF pixels to CoCo colors
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146 lbsr convline Convert the pixels to bytes.
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147 lbsr outline If we're done, output the line.
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148 lbsr clrline
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149 outpix7
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150 lbsr setline
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151 leax linebuff,y
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152 stx lineptr
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153 ldx <gifiwidth
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154 stx pixleft
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155 ldx #00
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156 stx horscale
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157
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158 ldd #0
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159 subd <Skipcols
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160 std pixcnt
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161 outpix9
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162 puls a,b,x,pc
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163
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164 dithline
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165 pshs a,b,x,y,u
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166 leau alt2buff,y Color mapping table.
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167 ldd pixscrn Number of pixels on this line.
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168 lsra Divide by 4, since main loop does 4 pixels at a time.
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169 rorb
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170 lsra
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171 rorb
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172 pshs b Even for a 640-pixel line, this will be less than 256.
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173 leay linebuff,y Y points to line data.
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174
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175 lda linenumb+1 What line (mod 4) are we on?
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176 anda #3
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177 leax dithtable,pcr
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178 leax a,x
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179 jsr a,x
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180 puls b
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181 puls a,b,x,y,u,pc
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182
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183 dithtable
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184 bra dithloop1 Different sub for each line (mod 4).
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185 bra dithloop2
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186 bra dithloop3
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187 bra dithloop4
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188
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189 dithloop1
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190 bsr dofastdith
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191 ldb #$60
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192 bsr dodither
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193 bsr dofastdith
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194 ldb #$40
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195 bsr dodither
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196 dec 3,s
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197 bne dithloop1
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198 rts
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199
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200 dithloop2
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201 ldb #$20
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202 bsr dodither
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203 bsr dofastdith
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204 ldb #$00
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205 bsr dodither
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206 bsr dofastdith
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207 dec 3,s
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208 bne dithloop2
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209 rts
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210
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211 dithloop3
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212 bsr dofastdith
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213 ldb #$50
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214 bsr dodither
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215 bsr dofastdither
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216 ldb #$70
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217 bsr dodither
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218 dec 3,s
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219 bne dithloop3
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220 rts
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221
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222 dithloop4
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223 ldb #$10
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224 bsr dodither
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225 bsr dofastdith
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226 ldb #$30
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227 bsr dodither
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228 bsr dofastdith
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229 dec 3,s
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230 bne dithloop4
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231 rts
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232
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233 * Dither one pixel. Get GIF color from ,y and convert it into primary
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234 * color iff B is above the threshold value.
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235 dodither
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236 pshs b
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237 ldb ,y
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238 clra
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239 leax d,u
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240 abx
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241 abx
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242 lda ,x Get primary color.
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243 puls b
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244 cmpb 2,x Are we above the threshold?
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245 bhs dodither1
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246 lda 1,x If not, choose secondary color.
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247 dodither1
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248 anda #$0f
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249 sta ,y+ Store the color.
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250 rts
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251
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252 * Since every other pixel is gauranteed to be a primary color, it seems
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253 * worthwhile to have a faster version of the dither sub for that case.
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254 dofastdith
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255 ldb ,y
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256 clra
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257 leax d,u
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258 abx
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259 lda d,x Get primary color.
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260 anda #$0f
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261 sta ,y+ Store the color.
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262 rts
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263
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264 convline
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265 pshs a,b,x,y,u
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266 lda <type
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267 cmpa #8
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268 bne conv4no
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269 bsr conv4line Type 8 screen has 4 bits/pixel
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270 bra conv10
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271 conv4no
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272 cmpa #7
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273 beq conv2
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274 cmpa #6
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275 bne conv2no
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276 conv2
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277 bsr conv2line type 7,6 are 2 bits/pix
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278 bra conv10
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279 conv2no
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280 bsr conv1line type 5 is 1 bit/pix
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281 conv10
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282 puls a,b,x,y,u,pc
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283
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284 conv4table fcb $00,$10,$20,$30,$40,$50,$60,$70,$80,$90,$a0,$b0,$c0,$d0,$e0,$f0
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285 conv4line
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286 leax linebuff,y
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287 tfr x,u
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288 leay conv4table,pcr
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289 ldb #160
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290 pshs b
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291 conv4loop
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292 lda ,x+
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293 ldb ,x+
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294 orb a,y
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295 stb ,u+
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296 dec ,s
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297 bne conv4loop
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298 puls b
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299 rts
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300
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301 conv2table fcb $00,$40,$80,$c0,$00,$10,$20,$30,$00,$04,$08,$0c
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302 conv2line
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303 leax linebuff,y
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304 tfr x,u
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305 leay conv2table,pcr
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306 ldd pixscrn
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307 lsra
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308 rorb
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309 lsra
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310 rorb
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311 pshs b
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312 conv2loop
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313 lda ,x+
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314 lda a,y Convert 1st pixel in byte.
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315 ldb ,x+
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316 addb #4
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317 ora b,y
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318 ldb ,x+
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319 addb #8
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320 ora b,y
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321 ora ,x+
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322 sta ,u+
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323 dec ,s
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324 bne conv2loop
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325 puls b
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326 rts
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327
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328 conv1line
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329 leax linebuff,y
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330 tfr x,u
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331 ldy #80
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332 conv1loop
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333 ldb #$80
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334 pshs b
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335 clra
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336 conv10loop
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337 tst ,x+
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338 beq conv11
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339 ora ,s
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340 conv11
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341 ror ,s
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342 bne conv10loop
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343 puls b
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344 sta ,u+
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345 leay -1,y
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346 bne conv1loop
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347 rts
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348
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349 clrline
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350 pshs a,b,x,y
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351 leax linebuff,y
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352 ldy pixscrn
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353 clra
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354 clrline1
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355 sta ,x+
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356 leay -1,y
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357 bne clrline1
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358 puls a,b,x,y,pc
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359
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360 nextline
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361 pshs d,x,u
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362 ldx lineinc
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363 beq nextline9
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364 ldd verscale
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365 nextline1
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366 tsta Actually, test sign of D
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367 bmi nextline2
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368 subd <gifiheight If it's positive, that's another screen line.
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369 ldu linenumb
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370 leau 1,u
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371 stu linenumb
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372 bra nextline1
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373 nextline2
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374 addd linemax
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375 ldu linecount That's another gif line.
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376 leau 1,u
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377 stu linecount
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378 leax -1,x
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379 bne nextline1
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380 std verscale
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381 nextline9
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382 puls d,x,u,pc
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383
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384 setline
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385 pshs a,b,x
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386 bsr nextline
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387 ldd linecount
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388 cmpd <gifiheight
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389 blo setline5
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390 andb #$7
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391 beq setline3
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392 ldd lineinc
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393 lsrb
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394 std lineinc
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395 setline3
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396 ldd #0
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397 std linecount
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398 std linenumb
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399 std verscale
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400 ldd lineinc
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401 lsrb
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402 clra
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403 std lineinc Start off by moving 1/2 of the increment
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404 bsr nextline
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405 lslb
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406 std lineinc Now, set the increment right.
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407 setline5
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408 puls a,b,x,pc
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409
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410 outline
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411 pshs a,b,x
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412 ldd linenumb
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413 subd <Skiplines
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414 bmi outline1
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415 cmpd #192
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416 bhs outline1
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417 lbsr putline Put the line onto the screen
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418 outline1
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419 puls a,b,x,pc
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420
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421 endsect
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