mirror of
https://github.com/sehugg/8bitworkshop.git
synced 2024-12-22 12:30:01 +00:00
200 lines
4.0 KiB
C
200 lines
4.0 KiB
C
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#include <string.h>
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#include "scrolling.h"
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sbyte scroll_fine_x;
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sbyte scroll_fine_y;
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byte origin_x;
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byte origin_y;
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byte* hidbuf;
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byte* visbuf;
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byte colorbuf[COLS*ROWS];
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byte swap_needed;
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byte copy_needed;
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//
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void scroll_swap() {
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byte* tmp;
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// swap hidden and visible buffers
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tmp = hidbuf;
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hidbuf = visbuf;
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visbuf = tmp;
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// set VIC bank address
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SET_VIC_SCREEN((word)visbuf);
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}
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void copy_color_ram_slow() {
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memcpy(COLOR_RAM, colorbuf, COLS*ROWS);
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}
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void copy_color_ram_fast() {
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// fast copy loop for upper 1/2 of color ram
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asm("ldy #0");
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asm("@loop:");
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asm("lda %v,y", colorbuf);
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asm("sta $d800,y");
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asm("lda %v + $100,y", colorbuf);
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asm("sta $d900,y");
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asm("iny");
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asm("bne @loop");
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// second loop for lower 1/2 of color ram
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asm("@loop2:");
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asm("lda %v + $200,y", colorbuf);
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asm("sta $da00,y");
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asm("lda %v + $300,y", colorbuf);
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asm("sta $db00,y");
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asm("@skip: iny");
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asm("bne @loop2");
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}
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void copy_to_hidden_buffer_slow() {
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memcpy(hidbuf, visbuf, COLS*ROWS);
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}
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void copy_to_hidden_buffer_fast() {
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// self-modifying code
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asm("ldy %v+1", visbuf);
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asm("sty @loop+2+6*0");
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asm("iny");
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asm("sty @loop+2+6*1");
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asm("iny");
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asm("sty @loop+2+6*2");
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asm("iny");
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asm("sty @skip-1-3");
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asm("ldy %v+1", hidbuf);
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asm("sty @loop+5+6*0");
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asm("iny");
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asm("sty @loop+5+6*1");
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asm("iny");
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asm("sty @loop+5+6*2");
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asm("iny");
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asm("sty @skip-1");
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// fast copy loop
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asm("ldy #0");
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asm("@loop:");
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asm("lda $8000,y");
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asm("sta $8000,y");
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asm("lda $8100,y");
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asm("sta $8100,y");
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asm("lda $8200,y");
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asm("sta $8200,y");
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asm("cpy #$e8");
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asm("bcs @skip");
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asm("lda $8300,y");
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asm("sta $8300,y");
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asm("@skip: iny");
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asm("bne @loop");
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}
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void copy_if_needed() {
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if (copy_needed) {
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copy_to_hidden_buffer_fast();
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copy_needed = false;
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}
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}
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void scroll_update() {
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SET_SCROLL_X(scroll_fine_x);
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SET_SCROLL_Y(scroll_fine_y);
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if (swap_needed) {
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scroll_swap();
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copy_color_ram_fast();
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swap_needed = false;
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copy_needed = true;
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} else {
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copy_if_needed();
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}
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}
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static void scroll_left() {
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copy_if_needed();
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memmove(hidbuf, hidbuf+1, COLS*ROWS-1);
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memmove(colorbuf, colorbuf+1, COLS*ROWS-1);
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++origin_x;
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scroll_draw_column(COLS-1);
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swap_needed = true;
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}
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static void scroll_up() {
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copy_if_needed();
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memmove(hidbuf, hidbuf+COLS, COLS*(ROWS-1));
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memmove(colorbuf, colorbuf+COLS, COLS*(ROWS-1));
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++origin_y;
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scroll_draw_row(ROWS-1);
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swap_needed = true;
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}
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static void scroll_right() {
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copy_if_needed();
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memmove(hidbuf+1, hidbuf, COLS*ROWS-1);
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memmove(colorbuf+1, colorbuf, COLS*ROWS-1);
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--origin_x;
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scroll_draw_column(0);
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swap_needed = true;
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}
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static void scroll_down() {
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copy_if_needed();
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memmove(hidbuf+COLS, hidbuf, COLS*(ROWS-1));
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memmove(colorbuf+COLS, colorbuf, COLS*(ROWS-1));
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--origin_y;
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scroll_draw_row(0);
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swap_needed = true;
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}
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void scroll_horiz(sbyte delta_x) {
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scroll_fine_x += delta_x;
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while (scroll_fine_x < 0) {
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scroll_fine_x += 8;
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scroll_left();
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}
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while (scroll_fine_x >= 8) {
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scroll_fine_x -= 8;
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scroll_right();
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}
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}
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void scroll_vert(sbyte delta_y) {
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scroll_fine_y += delta_y;
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while (scroll_fine_y < 0) {
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scroll_fine_y += 8;
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scroll_up();
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}
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while (scroll_fine_y >= 8) {
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scroll_fine_y -= 8;
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scroll_down();
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}
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}
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void scroll_xy(sbyte delta_x, sbyte delta_y) {
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if (delta_x) scroll_horiz(delta_x);
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if (delta_y) scroll_vert(delta_y);
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}
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void scroll_setup() {
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scroll_fine_x = scroll_fine_y = 0;
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origin_x = origin_y = 0;
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swap_needed = true;
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copy_needed = true;
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// setup screen buffer addresses
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hidbuf = (byte*) 0x8000;
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visbuf = (byte*) 0x8400;
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// copy existing screen contents to hidden buffer
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memcpy(hidbuf, (byte*)0x400, COLS*ROWS);
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// copy also to hidden buffer
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memcpy(visbuf, hidbuf, COLS*ROWS);
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// set VIC bank ($8000-$BFFF)
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// https://www.c64-wiki.com/wiki/VIC_bank
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SET_VIC_BANK(0x8000);
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// set up 24 line / 38 column mode to hide edges
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VIC.ctrl1 &= ~0x08; // 24 lines
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VIC.ctrl2 &= ~0x08; // 38 columns
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}
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