amigaos-cross-toolchain6/test/test2/test.c

typedef short int int16_t;
typedef unsigned short int uint16_t;
typedef unsigned long uint32_t;

#define PALETTE_NUM_FADE_STEPS 16
#define _PALETTE_RED(x) ((x >> 8) & 0xf)
#define _PALETTE_GREEN(x) ((x >> 4) & 0xf)
#define _PALETTE_BLUE(x) ((x) & 0xf)
#define _PALETTE_FIXED 8

typedef struct {
  uint16_t color[32];
} custom_t;

extern volatile custom_t* custom;

extern void hw_waitVerticalBlank();

extern uint16_t palette_background;

void
palette_fadeTo(uint16_t* palette, uint16_t colors, uint16_t color)
{
  int fr = _PALETTE_RED(color) << 4;
  int fg = _PALETTE_GREEN(color) << 4;
  int fb = _PALETTE_BLUE(color) << 4;
  
  for (int i = 0; i < PALETTE_NUM_FADE_STEPS; i++) {
    for (int c = 0; c < colors; c++) {

      int tr = _PALETTE_RED(palette[c]);
      int tg = _PALETTE_GREEN(palette[c]);
      int tb = _PALETTE_BLUE(palette[c]);            
      
      int nr = ((fr<<_PALETTE_FIXED)+((((tr<<_PALETTE_FIXED)-(fr<<_PALETTE_FIXED))/PALETTE_NUM_FADE_STEPS)*i))>>_PALETTE_FIXED;
      int ng = ((fg<<_PALETTE_FIXED)+((((tg<<_PALETTE_FIXED)-(fg<<_PALETTE_FIXED))/PALETTE_NUM_FADE_STEPS)*i))>>_PALETTE_FIXED;
      int nb = ((fb<<_PALETTE_FIXED)+((((tb<<_PALETTE_FIXED)-(fb<<_PALETTE_FIXED))/PALETTE_NUM_FADE_STEPS)*i))>>_PALETTE_FIXED;      

      custom->color[c] = (nr<<8)|(ng<<4)|nb;
    }

    hw_waitVerticalBlank();
  }

  for (int c = 0; c < colors; c++) {
    custom->color[c] = palette[c];
  }

  palette_background = palette[0];
}