cool-bun-demo/bun.c

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

// WaitBlit()
#include <clib/graphics_protos.h>

// AllocMem(), FreeMem()
#include <clib/exec_protos.h>
#include <exec/memory.h>

#include "screen.h"
#include "bun.h"
#include "system/system.h"

// linked as raw bytes in assembler
extern unsigned char far coolbun[];

unsigned char *coolbunArea;

#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))

extern struct Custom far custom;

void setupBun() {
  unsigned char *currentCoolBunArea, *currentCoolBun;
  unsigned int x, y, plane;

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

  CopyMem(coolbun, coolbunArea, COOL_BUN_MEMORY_SIZE);
}

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

void bun_offRightSide(
  int plusXValue,
  int y,
  struct ScreenSetup *screenSetup,
  struct CurrentScreen *currentScreen
) {
  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 = BLTCON0(0xc0, 0, 1, 0, 1, shift);
    custom.bltcon1 = BLTCON1(0, shift);

    custom.bltadat = 0xffff;
    custom.bltbpt = coolbunArea +
      plane * COOL_BUN_PLANE_SIZE;
    custom.bltdpt = currentScreen->planes[plane] +
      (y * screenSetup->byteWidth) +
      screenSetup->byteWidth - COOL_BUN_WIDTH_BYTES +
      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->byteWidth - COOL_BUN_WIDTH_BYTES +
      wordShift * 2;

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

    WaitBlit();
  }
}

void bun_offLeftSide(
  int minusXValue,
  int y,
  struct ScreenSetup *screenSetup,
  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_LAST_ROW_BYTES +
      plane * COOL_BUN_PLANE_SIZE;

    // d is the part on screen
    custom.bltdpt = currentScreen->planes[plane] +
      (screenSetup->byteWidth * (y + COOL_BUN_LAST_ROW)) +
      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->byteWidth - 4 + wordShift * 2;

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

    WaitBlit();
  }
}

void bun_anywhere(
  int x,
  int y,
  struct ScreenSetup *screenSetup,
  struct CurrentScreen *currentScreen
) {
  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 = BLTCON0(0xc0, 0, 1, 0, 1, shift);
    custom.bltcon1 = BLTCON1(0, shift);

    custom.bltadat = 0xffff;
    custom.bltbpt = coolbunArea + plane * COOL_BUN_PLANE_SIZE;
    custom.bltdpt = currentScreen->planes[plane] +
      WORD_ALIGNED_BYTE_POSITION(screenSetup->width, x, y);

   // custom.bltdpt = screenSetup.memoryStart;
    custom.bltafwm = 0xffff;
    if (needsExtraWord) {
      custom.bltalwm = 0x0000;
    } else {
      custom.bltalwm = 0xffff;
    }

    custom.bltbmod = -(needsExtraWord * 2);
    custom.bltdmod = screenSetup->byteWidth - COOL_BUN_WIDTH_BYTES - (needsExtraWord * 2);
    custom.bltsize = (2 + needsExtraWord) + (COOL_BUN_HEIGHT << 6);

    WaitBlit();
  }
}

void renderBun(
  int x,
  int y,
  struct ScreenSetup *screenSetup,
  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 > screenSetup->width + 31) return;
  if (y < 1) return;
  if (y > screenSetup->height- COOL_BUN_HEIGHT - 1) return;

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