59 lines
1.4 KiB
C
59 lines
1.4 KiB
C
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#include "common.h"
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//#link "common.c"
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#include <cbm_petscii_charmap.h>
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#define BUFFER_0 0x400
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#define BUFFER_1 0x3c00
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byte scroll_x = 0; // x scroll position
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byte* scrnbuf[2]; // screen buffer(s)
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byte visbuf; // which buffer is visible? 0 or 1
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void scroll_one_pixel_left() {
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byte* src;
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byte* dst;
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// scroll left
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scroll_x--;
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// set scroll registers
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SET_SCROLL_X(scroll_x);
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// calculate frame pointers
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// source = visible buffer
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src = scrnbuf[visbuf] + (scroll_x & 7) * 128;
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// destination = hidden buffer
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dst = scrnbuf[visbuf ^ 1] + (scroll_x & 7) * 128;
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// wait for end of frame
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wait_vblank();
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// scroll hidden buffer
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memcpy(dst, src+1, 128);
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// every 8 pixels, switch visible and hidden buffers
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// and set VIC to point to other buffer
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if ((scroll_x & 7) == 0) {
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visbuf ^= 1;
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SET_VIC_SCREEN(visbuf ? BUFFER_1 : BUFFER_0);
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}
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}
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void main(void) {
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clrscr();
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printf("\n\n\n Hello Scrolling World!");
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printf("\n\n\n We scroll in one direction");
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printf("\n\n\n And now we have two buffers");
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printf("\n\n\n And copy hidden -> visible");
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printf("\n\n\n 128 bytes (of 1024) per frame");
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VIC.ctrl1 = 0x10; // 24 lines
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VIC.ctrl2 = 0x00; // 38 columns
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VIC.bordercolor = COLOR_GRAY1;
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// get screen buffer addresses
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scrnbuf[0] = (byte*) BUFFER_0;
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scrnbuf[1] = (byte*) BUFFER_1;
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// infinite loop
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while (1) {
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scroll_one_pixel_left();
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}
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}
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