1 | | ------------------------------------------------------------------------------
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2 | | vputp.s -- put a pixel into a 4-bit per pixel bitmap object
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3 | | Version 4 -- 1987-08-04 -- D.N. Lynx Crowe
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4 | | (c) Copyright 1987 -- D.N. Lynx Crowe
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5 | | ------------------------------------------------------------------------------
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6 | | int
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7 | | vputp(octad, xloc, yloc, val)
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8 | | struct octent |octad;
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9 | | int xloc, yloc;
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10 |
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11 | | Puts the pixel value 'val' at ('xloc','yloc') in the
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12 | | 4-bit per pixel bitmap object described by 'octad'.
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13 |
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14 | | -----
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15 | | struct octent {
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16 |
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17 | | uint ysize,
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18 | | xsize;
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19 |
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20 | | int objx,
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21 | | objy;
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22 |
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23 | | uint |obase;
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24 |
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25 | | char opri,
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26 | | obank;
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27 |
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28 | | uint odtw0,
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29 | | odtw1;
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30 | | };
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31 |
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32 | .text
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33 |
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34 | .xdef _vputp
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35 |
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36 | OCTAD = 8
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37 | XLOC = 12
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38 | YLOC = 14
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39 | VAL = 16
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40 |
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41 | YSIZE = 0
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42 | XSIZE = 2
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43 | OBJX = 4
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44 | OBJY = 6
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45 | OBASE = 8
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46 | OPRI = 12
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47 | OBANK = 13
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48 | ODTW0 = 14
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49 | ODTW1 = 16
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50 |
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51 | .page
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52 |
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53 | _vputp: link a6,#0 | Link stack frames
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54 | movea.l OCTAD(a6),a1 | Get OCTAD base into a1
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55 | move.w XLOC(a6),d0 | Get XLOC into d0
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56 | cmp.w XSIZE(a1),d0 | Check XLOC range
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57 | bge vputerr | ERROR if too large
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58 |
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59 | tst.w d0 | Check XLOC sign
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60 | bmi vputerr | ERROR if negative
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61 |
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62 | move.w YLOC(a6),d1 | Get YLOC into d1 to test
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63 | cmp.w YSIZE(a1),d1 | Check YLOC range
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64 | bge vputerr | ERROR if too large
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65 |
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66 | tst.w d1 | Check YLOC sign
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67 | bmi vputerr | ERROR if negative
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68 |
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69 | lsr.w #2,d0 | Divide XLOC by 4
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70 | move.w XSIZE(a1),d1 | Get width into d1
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71 | lsr.w #2,d1 | Divide width by 4
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72 | mulu YLOC(a6),d1 | Multiply width/4 by YLOC
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73 | ext.l d0 | Extend XLOC/4 to a long
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74 | add.l d0,d1 | ... and add it to d1
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75 | lsl.l #1,d1 | Make d1 a word offset
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76 | add.l OBASE(a1),d1 | Add OBASE to d1
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77 | movea.l d1,a0 | Make a0 point at bitmap data
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78 | move.w XLOC(a6),d0 | Get XLOC
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79 | andi.l #0x03,d0 | Mask to low 2 bits
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80 | add.l d0,d0 | Multiply by 2 for word index
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81 | move.l d0,d1 | Save index in d1
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82 | add.l #MTAB,d0 | Add mask table base
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83 | movea.l d0,a2 | a2 points at mask
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84 | add.l #STAB,d1 | Add shift table base to index
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85 | move.l d1,a1 | a1 points at shift count
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86 | move.w (a1),d0 | Get shift count in d0
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87 | move.w VAL(a6),d1 | Get new pixel in d1
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88 | andi.w #0x0F,d1 | Mask down to 4 bits
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89 | lsl.w d0,d1 | Shift into position for OR
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90 | move.w (a0),d0 | Get old bitmap word in d0
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91 | and.w (a2),d0 | Mask out old pixel
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92 | or.w d1,d0 | OR in new pixel
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93 | move.w d0,(a0) | Store updated word in bitmap
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94 | clr.l d0 | Set return value = 0 = OK
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95 |
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96 | vputexit: unlk a6 | Unlink stack frame
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97 | rts | Return to caller
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98 |
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99 | vputerr: moveq.l #-1,d0 | Set return value = -1 = ERROR
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100 | bra vputexit | Go unlink stack and return
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101 |
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102 | .page
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103 |
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104 | .data
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105 |
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106 | MTAB: dc.w 0xFFF0,0xFF0F,0xF0FF,0x0FFF | Mask table
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107 | STAB: dc.w 0,4,8,12 | Shift table
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108 |
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109 | .end
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