101screen.subx

   1 # Primitives for screen control.
   2 #
   3 # We need to do this in machine code because Mu doesn't have global variables
   4 # yet (for the start of video memory).
   5
   6 == code
   7
   8 pixel-on-real-screen:  # x: int, y: int, color: int
   9     # . prologue
  10     55/push-ebp
  11     89/<- %ebp 4/r32/esp
  12     #
  13     (pixel-on-screen-buffer *Video-memory-addr *(ebp+8) *(ebp+0xc) *(ebp+0x10) 0x400 0x300)
  14 $pixel-on-real-screen:end:
  15     # . epilogue
  16     89/<- %esp 5/r32/ebp
  17     5d/pop-to-ebp
  18     c3/return
  19
  20 # 'buffer' here is not a valid Mu type: a naked address without a length.
  21 pixel-on-screen-buffer:  # buffer: (addr byte), x: int, y: int, color: int, width: int, height: int
  22     # . prologue
  23     55/push-ebp
  24     89/<- %ebp 4/r32/esp
  25     # . save registers
  26     50/push-eax
  27     51/push-ecx
  28     # bounds checks
  29     8b/-> *(ebp+0xc) 0/r32/eax  # foo
  30     3d/compare-eax-and 0/imm32
  31     7c/jump-if-< $pixel-on-screen-buffer:end/disp8
  32     3b/compare 0/r32/eax *(ebp+0x18)
  33     7d/jump-if->= $pixel-on-screen-buffer:end/disp8
  34     8b/-> *(ebp+0x10) 0/r32/eax
  35     3d/compare-eax-and 0/imm32
  36     7c/jump-if-< $pixel-on-screen-buffer:end/disp8
  37     3b/compare 0/r32/eax *(ebp+0x1c)
  38     7d/jump-if->= $pixel-on-screen-buffer:end/disp8
  39     # eax = y*width + x
  40     8b/-> *(ebp+0x10) 0/r32/eax
  41     0f af/multiply-> *(ebp+0x18) 0/r32/eax
  42     03/add-> *(ebp+0xc) 0/r32/eax
  43     # eax += location of frame buffer
  44     03/add-> *(ebp+8) 0/r32/eax
  45     # *eax = color
  46     8b/-> *(ebp+0x14) 1/r32/ecx
  47     88/byte<- *eax 1/r32/CL
  48 $pixel-on-screen-buffer:end:
  49     # . restore registers
  50     59/pop-to-ecx
  51     58/pop-to-eax
  52     # . epilogue
  53     89/<- %esp 5/r32/ebp
  54     5d/pop-to-ebp
  55     c3/return