cool-bun-demo/bun.c

#include "screen.h"
#include "bun.h"

extern unsigned char far coolbun[];

unsigned char *coolbunArea;

#define COOL_BUN_WIDTH (32)
#define COOL_BUN_WIDTH_BYTES (COOL_BUN_WIDTH / 8)
#define COOL_BUN_HEIGHT (32)
#define COOL_BUN_PLANES (2)

#define COOL_BUN_PLANE_SIZE (COOL_BUN_WIDTH_BYTES * COOL_BUN_HEIGHT)
#define COOL_BUN_MEMORY_SIZE (COOL_BUN_PLANE_SIZE * COOL_BUN_PLANES)

void setupBun() {
  unsigned char *currentCoolBunArea, *currentCoolBun;

  coolbunArea = AllocMem(COOL_BUN_MEMORY_SIZE, MEMF_CHIP | MEMF_CLEAR);
  currentCoolBun = coolbun;

  currentCoolBunArea = coolbunArea;

  for (plane = 0; plane < COOL_BUN_PLANES; ++plane) {
    for (y = 0; y < COOL_BUN_HEIGHT; ++y) {
      for (x = 0; x < COOL_BUN_WIDTH_BYTES; ++x) {
        *(currentCoolBunArea++) = *(currentCoolBun++);
      }
    }
  }
}

void teardownBun() {
  FreeMem(coolbunArea, COOL_BUN_MEMORY_SIZE);
}

void bun_offRightSide(int plusXValue, int y, struct ScreenSetup *screenSetup) {
  uint8_t i, plane = 0;
  uint8_t shift = plusXValue & 15;
  uint8_t wordShift = (plusXValue >> 4);
  uint16_t bltalwm;

  for (plane = 0; plane < 2; ++plane) {
    custom.bltcon0 = 0xc0 + (1 << 8) + (1 << 10) + (shift << 12);
    custom.bltcon1 = (shift << 12);

    custom.bltadat = 0xffff;
    custom.bltbpt = coolbunArea + plane * COOL_BUN_PLANE_SIZE;
    custom.bltdpt = screenSetup->memoryStart +
      plane * screenSetup->nextBitplaneAdvance +
      (y * screenSetup.width + screenSetup.width - COOL_BUN_WIDTH) / 8
      + wordShift * 2;

    custom.bltafwm = 0xffff;
    bltalwm = 0x0000;
    for (i = 0; i < 15 - shift; ++i) {
      bltalwm += (1 << (15 - i));
    }
    custom.bltalwm = bltalwm;

    custom.bltbmod = wordShift * 2;
    custom.bltdmod = (screenSetup.width - COOL_BUN_WIDTH) / 8 + wordShift * 2;

    custom.bltsize = 2 - wordShift + (COOL_BUN_HEIGHT << 6);

    WaitBlit();
  }
}

#define BLTCON0( \
  minterm, aChan, bChan, cChan, dChan, shift \
) (minterm + (aChan << 11) + (bChan << 10) + (cChan << 9) + (dChan << 8) + (shift << 12)
#define BLTCON1(descending, shift) ((descending << 1) + (shift << 12))

void bun_offLeftSide(int minusXValue, int y, struct CurrentScreen *currentScreen) {
  unsigned char plane;
  uint8_t shift = minusXValue & 15;
  uint8_t wordShift = (minusXValue >> 4);
  uint8_t i;
  uint16_t bltalwm;

  // y can't be 0 otherwise we will corrupt memory for now
  if (y == 0) return;

  for (plane = 0; plane < 2; ++plane) {
    // shift left, so descending
    custom.bltcon0 = BLTCON0(0xc0, 0, 1, 0, 1, shift);
    custom.bltcon1 = BLTCON1(1, shift);

    // a has a mask we're shifting
    custom.bltadat = 0xffff;
    // b has bun data
    custom.bltbpt = coolbunArea + 2 + ((COOL_BUN_HEIGHT - 1) * 4) + plane * COOL_BUN_PLANE_SIZE;

    // d is the part on screen
    custom.bltdpt = screenSetup.memoryStart + screenSetup.nextBitplaneAdvance * plane + (screenSetup.width * (y + COOL_BUN_HEIGHT - 1) / 8) + 2 - wordShift * 2;

    custom.bltafwm = 0xffff;
    bltalwm = 0x0000;
    for (i = 0; i < 15 - shift; ++i) {
      bltalwm += (1 << i);
    }
    custom.bltalwm = bltalwm;

    custom.bltbmod = wordShift * 2;
    custom.bltdmod = screenSetup.width / 8 - 4 + wordShift * 2;

    custom.bltsize = 2 - wordShift + (COOL_BUN_HEIGHT << 6);

    WaitBlit();
  }
}

void bun_anywhere(int x, int y, struct ScreenSetup *screenSetup) {
  uint8_t plane;
  uint8_t shift = x & 15;
  uint8_t needsExtraWord = shift != 0;

  for (plane = 0; plane < 2; ++plane) {
    // if we extend the bun area by a word, we only need one write

    // buns will never interfere with a background so they don't need a mask
    // they do need the scratch area though
    custom.bltcon0 = 0xc0 + (1 << 8) + (1 << 10) + (shift << 12);
    custom.bltcon1 = (shift << 12);

    custom.bltadat = 0xffff;
    custom.bltbpt = coolbunArea + plane * COOL_BUN_PLANE_SIZE;
    custom.bltdpt = screenSetup.memoryStart + WORD_ALIGNED_BYTE_POSITION(screenSetup.width, x, y) + screenSetup.nextBitplaneAdvance * plane;

   // custom.bltdpt = screenSetup.memoryStart;
    custom.bltafwm = 0xffff;
    if (needsExtraWord) {
      custom.bltalwm = 0x0000;
    } else {
      custom.bltalwm = 0xffff;
    }
    custom.bltbmod = -(needsExtraWord * 2);
    custom.bltdmod = (screenSetup.width / 8) - COOL_BUN_WIDTH_BYTES - (needsExtraWord * 2);
    custom.bltsize = (2 + needsExtraWord) + (COOL_BUN_HEIGHT << 6);

    WaitBlit();
  }
}

void renderBun(int x, int y, struct CurrentScreen *currentScreen) {
  /**
    * Conditions that will cause the program to crash if met. If your bun
    * isn't rendering, it's due to here.
    *
    * TODO: Handle top/bottom off-screen as well.
    */
  if (x < -31) return;
  if (x > currentScreen->pixelWidth + 31) return;
  if (y < 1) return;
  if (y > currentScreen->pixelHeight- COOL_BUN_HEIGHT - 1) return;

  if (x < 0) {
    bun_offLeftSide(-x, y, currentScreen);
  } else if (x > screenSetup.width - COOL_BUN_WIDTH) {
    bun_offRightSide(x - (currentScreen->pixelWidth - COOL_BUN_WIDTH), y, currentScreen);
  } else {
    bun_anywhere(x, y, currentScreen);
  }
}