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collapseos/emul/z80/sms_vdp.c
Virgil Dupras 490eceab6d emul/z80: flatten directory structure
I'm about to reuse sdc.c in sms.c and the old directory structure
was becoming awkward.
2020-10-25 15:58:00 -04:00

84 lines
2.2 KiB
C

#include <string.h>
#include "sms_vdp.h"
void vdp_init(VDP *vdp)
{
memset(vdp->vram, 0, VDP_VRAM_SIZE);
memset(vdp->regs, 0, 0x10);
vdp->has_cmdlsb = false;
vdp->curaddr = 0;
}
uint8_t vdp_cmd_rd(VDP *vdp)
{
return 0;
}
void vdp_cmd_wr(VDP *vdp, uint8_t val)
{
if (!vdp->has_cmdlsb) {
vdp->cmdlsb = val;
vdp->has_cmdlsb = true;
return;
}
vdp->has_cmdlsb = false;
if ((val & 0xc0) == 0x80) {
// set register
vdp->regs[val&0xf] = vdp->cmdlsb;
} else if ((val & 0xc0) == 0xc0) {
// palette RAM
vdp->curaddr = 0x4000 + (vdp->cmdlsb&0x1f);
} else {
// VRAM
vdp->curaddr = ((val&0x3f) << 8) + vdp->cmdlsb;
}
}
uint8_t vdp_data_rd(VDP *vdp)
{
uint8_t res = vdp->vram[vdp->curaddr];
if (vdp->curaddr < VDP_VRAM_SIZE) {
vdp->curaddr++;
}
return res;
}
void vdp_data_wr(VDP *vdp, uint8_t val)
{
vdp->vram[vdp->curaddr] = val;
if (vdp->curaddr < VDP_VRAM_SIZE) {
vdp->curaddr++;
}
}
// Returns a 8-bit RGB value (0b00bbggrr)
uint8_t vdp_pixel(VDP *vdp, uint16_t x, uint16_t y)
{
if (x >= VDP_SCREENW) {
return 0;
}
if (y >= VDP_SCREENH) {
return 0;
}
// name table offset
uint16_t offset = (vdp->regs[2] & 0xe) << 10;
offset += ((y/8) << 6) + ((x/8) << 1);
uint16_t tableval = vdp->vram[offset] + (vdp->vram[offset+1] << 8);
uint16_t tilenum = tableval & 0x1ff;
// is palette select bit on? if yes, use sprite palette instead
uint8_t palettemod = tableval & 0x800 ? 0x10 : 0;
// tile offset this time. Each tile is 0x20 bytes long.
offset = tilenum * 0x20;
// Each 4 byte is a row. Find row first.
offset += ((y%8) * 4);
uint8_t bitnum = 7 - (x%8);
// Now, let's compose the result by pushing the right bit of our 4 bytes
// into our result.
uint8_t palette_id = ((vdp->vram[offset] >> bitnum) & 1) + \
(((vdp->vram[offset+1] >> bitnum) & 1) << 1) + \
(((vdp->vram[offset+2] >> bitnum) & 1) << 2) + \
(((vdp->vram[offset+3] >> bitnum) & 1) << 3);
uint8_t rgb = vdp->vram[0x4000+palettemod+palette_id];
return rgb;
}