mirror of
https://github.com/sehugg/8bitworkshop.git
synced 2024-12-23 03:29:39 +00:00
282 lines
5.8 KiB
C
282 lines
5.8 KiB
C
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#include <string.h>
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#include "scrolling.h"
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#define VICBANK 0x8000
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#define BUFFER_A (byte*) 0x8000
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#define BUFFER_B (byte*) 0x8400
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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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int pixofs_x;
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int pixofs_y;
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sbyte fine_correct_x;
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sbyte fine_correct_y;
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byte scroll_dir;
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byte scroll_seq;
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//
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static void wait_offscreen(void) {
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while (VIC.rasterline < 250 && VIC.rasterline > 40) ;
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}
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void scroll_swap(void) {
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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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wait_offscreen();
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VIC.addr = (VIC.addr & 0xf) | (((word)visbuf >> 8) << 2);
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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 scroll_start(byte dir) {
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if (scroll_seq == 0 && dir) {
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scroll_dir = dir;
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scroll_seq = 8;
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// correct sprites b/c our fine offset is one pixel
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// off depending on last scroll direction
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if (dir & SCROLL_LEFT) fine_correct_x = 1;
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else if (dir & SCROLL_RIGHT) fine_correct_x = 0;
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if (dir & SCROLL_UP) fine_correct_y = 1;
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else if (dir & SCROLL_DOWN) fine_correct_y = 0;
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}
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}
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void scroll_step_move_buffer(char* src, char* dst) {
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word size = COLS*ROWS;
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if (scroll_dir & SCROLL_LEFT) {
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++src;
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--size;
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}
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if (scroll_dir & SCROLL_RIGHT) {
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++dst;
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--size;
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}
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if (scroll_dir & SCROLL_UP) {
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src += COLS;
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size -= COLS;
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}
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if (scroll_dir & SCROLL_DOWN) {
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dst += COLS;
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size -= COLS;
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}
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memmove(dst, src, size);
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}
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void scroll_step_draw_cells() {
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if (scroll_dir & SCROLL_UP) ++origin_y;
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if (scroll_dir & SCROLL_DOWN) --origin_y;
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if (scroll_dir & SCROLL_LEFT) {
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++origin_x;
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scroll_draw_column(COLS-1);
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}
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if (scroll_dir & SCROLL_RIGHT) {
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--origin_x;
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scroll_draw_column(0);
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}
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if (scroll_dir & SCROLL_UP) {
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scroll_draw_row(ROWS-1);
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}
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if (scroll_dir & SCROLL_DOWN) {
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scroll_draw_row(0);
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}
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}
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void scroll_step_move_sprites() {
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// copy sprites from visible to hidden buffer
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memcpy(hidbuf + 0x3f8, visbuf + 0x3f8, 8);
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}
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void scroll_update_pixofs() {
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// fine scroll starts at 8-5 = 32107 or 12-8 = 45670
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if (scroll_dir & SCROLL_LEFT) {
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pixofs_x -= 1;
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scroll_fine_x = (scroll_seq - 5) & 7;
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}
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if (scroll_dir & SCROLL_RIGHT) {
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pixofs_x += 1;
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scroll_fine_x = (12 - scroll_seq) & 7;
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}
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if (scroll_dir & SCROLL_UP) {
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pixofs_y -= 1;
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scroll_fine_y = (scroll_seq - 5) & 7;
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}
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if (scroll_dir & SCROLL_DOWN) {
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pixofs_y += 1;
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scroll_fine_y = (12 - scroll_seq) & 7;
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}
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}
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void scroll_offset_sprites(byte delta) {
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byte dx = 0;
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byte dy = 0;
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// fine scroll starts at 8-5 = 32107 or 12-8 = 45670
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if (scroll_dir & SCROLL_LEFT) {
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dx = -delta;
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}
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if (scroll_dir & SCROLL_RIGHT) {
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dx = delta;
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}
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if (scroll_dir & SCROLL_UP) {
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dy = -delta;
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}
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if (scroll_dir & SCROLL_DOWN) {
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dy = delta;
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}
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VIC.spr_pos[0].x += dx;
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VIC.spr_pos[1].x += dx;
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VIC.spr_pos[0].y += dy;
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VIC.spr_pos[1].y += dy;
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}
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void scroll_update_scroll_regs() {
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wait_offscreen();
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VIC.ctrl1 = (VIC.ctrl1 & 0xf8) | scroll_fine_y;
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VIC.ctrl2 = (VIC.ctrl2 & 0xf8) | scroll_fine_x;
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}
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void scroll_next_step(void) {
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switch (--scroll_seq) {
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case 7:
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scroll_step_move_buffer(visbuf, hidbuf);
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break;
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case 6:
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scroll_step_move_buffer(colorbuf, colorbuf);
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break;
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case 5:
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scroll_step_draw_cells();
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break;
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case 4:
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scroll_step_move_sprites();
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break;
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case 3:
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scroll_swap();
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copy_color_ram_fast();
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break;
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}
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}
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void scroll_update(void) {
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if (scroll_seq) {
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scroll_update_pixofs();
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scroll_update_scroll_regs();
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scroll_offset_sprites(1);
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scroll_next_step();
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}
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}
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void scroll_finish(void) {
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while (scroll_seq) {
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scroll_update_pixofs();
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if (scroll_seq == 4) { scroll_offset_sprites(8); }
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scroll_next_step();
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}
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}
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void scroll_setup(void) {
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origin_x = origin_y = 0;
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pixofs_x = pixofs_y = 0;
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scroll_fine_x = scroll_fine_y = 3;
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scroll_dir = 0;
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scroll_seq = 0;
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// setup screen buffer addresses
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hidbuf = BUFFER_A;
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visbuf = BUFFER_B;
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memset(BUFFER_A, 0, 0x800);
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memset(colorbuf, 0, sizeof(colorbuf));
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SET_VIC_BANK(VICBANK);
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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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void scroll_refresh(void) {
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byte i;
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for (i=0; i<25; i++) {
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scroll_draw_row(i);
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}
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scroll_swap();
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copy_color_ram_fast();
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copy_to_hidden_buffer_fast();
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scroll_dir = 0;
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scroll_seq = 0;
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scroll_fine_x = scroll_fine_y = 3;
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}
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