cool-bun-demo/system/blitter.c

#include <stdlib.h>
#include <hardware/custom.h>

#include "blitter.h"
#include "system.h"
#include "../types.h"

extern struct Custom far custom;

/**
 * @param setup Data about the line's draw properties are injected into this struct.
 */
void blit_calculateLineBlit(
  struct BlitDrawLineSetup *setup,
  uint16_t sx,
  uint16_t sy,
  uint16_t ex,
  uint16_t ey
) {
  uint16_t i;

  setup->sx = sx;
  setup->dx = ex - sx;
  setup->dy = ey - sy;

  if (setup->dx == 0 && setup->dy == 0) return;

  setup->sud = abs(setup->dy) < abs(setup->dx);
  if (!setup->sud) { i = setup->dx; setup->dx = setup->dy; setup->dy = i; }

  setup->sul = setup->dy < 0;
  setup->dy = abs(setup->dy);

  setup->aul = setup->dx < 0;
  setup->dx = abs(setup->dx);

  setup->accumulator = 4 * setup->dy - 2 * setup->dx;
  setup->sign = setup->accumulator < 0;
}

void blit_drawSingleLine(
  struct BlitAreaDetails *blitAreaDetails,
  struct BlitDrawLineSetup *setup
) {
    custom.bltadat = 0x8000;
    custom.bltbdat = setup->linePattern;

    custom.bltafwm = 0xffff;
    custom.bltalwm = 0xffff;

    custom.bltamod = 4 * (setup->dy - setup->dx);
    custom.bltbmod = 4 * setup->dy;
    custom.bltcmod = blitAreaDetails->drawAreaWidth / 8;
    custom.bltdmod = blitAreaDetails->drawAreaWidth / 8;

    custom.bltapt = setup->accumulator;
    custom.bltcpt = setup->target;
    custom.bltdpt = setup->target;

    custom.bltcon0 = ((setup->sx % 16) << 12) + (11 << 8) + 0xca;
    custom.bltcon1 = 1 + (setup->aul << 2) + (setup->sul << 3) + (setup->sud << 4) + (setup->sign << 6);

    custom.bltsize = 0x02 + ((setup->dx + 1) << 6);
}

void blit_drawLine(
  struct BlitAreaDetails *blitAreaDetails,
  struct BlitDrawLineSetup *setup,
  uint16_t sx,
  uint16_t sy,
  uint16_t ex,
  uint16_t ey,
  uint8_t color
) {
  int i;

  blit_calculateLineBlit(setup, sx, sy, ex, ey);
  setup->target = blitAreaDetails->target + WORD_ALIGNED_BYTE_POSITION(blitAreaDetails->drawAreaWidth, sx, sy);

  for (i = 0; i < blitAreaDetails->contiguousBitplanes; ++i) {
    setup->linePattern = ((color & 1) == 1) ? 0xffff : 0;

    blit_drawSingleLine(blitAreaDetails, setup);

    setup->target += blitAreaDetails->nextBitplaneAdvance;
    color >>= 1;

    WaitBlit();
  }
}

void blit_fillPolygon(
  struct ScreenSetup *screenSetup,
  uint16_t sx,
  uint16_t sy,
  uint16_t ex,
  uint16_t ey,
  uint8_t color
) {
  // use a standard copy blit
  // set bltadat to 0xffff
  // set bltdpt to the top left corner of the zone
  // width is dx / 8
  // height is dy
  // enable descending mode
  // enable inclusive fill for now

  uint16_t dx = ex - sx;
  uint16_t dy = ey - sy;

  unsigned char *source = screenSetup->memoryStart + ((((ey * screenSetup->width + ex) >> 3) - 2) & 0xfffe);
  unsigned char *target = screenSetup->memoryStart + (((((ey + 100) * screenSetup->width + ex) >> 3) - 2) & 0xfffe);

  custom.bltcon0 = (1 << 11) + (1 << 8) + 0xF0; // we don't want to copy anything so we only enable target
  custom.bltcon1 = (1 << 1) + (1 << 3);
  custom.bltapt = source;
  custom.bltdpt = target;
  custom.bltamod = ((screenSetup->width - dx) >> 3) + 1;
  custom.bltdmod = ((screenSetup->width - dx) >> 3) + 1;
  custom.bltafwm = 0xffff;
  custom.bltalwm = 0xffff;
  custom.bltsize = (dx / 16) + (dy << 6);
}