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8bitworkshop/presets/nes/vrambuf.c

50 lines
1.2 KiB
C

#include "neslib.h"
#include "vrambuf.h"
#include <string.h>
// index to end of buffer
byte updptr = 0;
// add EOF marker to buffer (but don't increment pointer)
void vrambuf_end(void) {
VRAMBUF_SET(NT_UPD_EOF);
}
// clear vram buffer and place EOF marker
void vrambuf_clear(void) {
updptr = 0;
vrambuf_end();
}
// wait for next frame, then clear buffer
// this assumes the NMI will call flush_vram_update()
void vrambuf_flush(void) {
// make sure buffer has EOF marker
vrambuf_end();
// wait for next frame to flush update buffer
// this will also set the scroll registers properly
ppu_wait_frame();
// clear the buffer
vrambuf_clear();
}
// add multiple characters to update buffer
// using horizontal increment
void vrambuf_put(word addr, register const char* str, byte len) {
// if bytes won't fit, wait for vsync and flush buffer
if (VBUFSIZE-4-len < updptr) {
vrambuf_flush();
}
// add vram address
VRAMBUF_ADD((addr >> 8) ^ NT_UPD_HORZ);
VRAMBUF_ADD(addr); // only lower 8 bits
// add length
VRAMBUF_ADD(len);
// add data to buffer
memcpy(updbuf+updptr, str, len);
updptr += len;
// place EOF mark
vrambuf_end();
}