139 lines
2.4 KiB
C
139 lines
2.4 KiB
C
#include <c64/vic.h>
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#include <c64/memmap.h>
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#include <string.h>
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#include <stdlib.h>
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// Screen and color space
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#define screen ((byte *)0x0400)
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#define color ((byte *)0xd800)
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// Macro for easy access to screen and color space
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#define sline(x, y) (screen + 40 * (y) + (x))
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#define cline(x, y) (color + 40 * (y) + (x))
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// Column buffer for one prepared column of screen and color data
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char rbuff[25], cbuff[25];
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// Split into three scrolling sections to race the beam
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#define SPLIT1 8
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#define SPLIT2 16
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// Scroll top section
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void scrollLeft0(void)
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{
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for(char x=0; x<39; x++)
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{
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#pragma unroll(full)
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for(char y=0; y<SPLIT1; y++)
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{
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sline(0, y)[x] = sline(1, y)[x];
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cline(0, y)[x] = cline(1, y)[x];
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}
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}
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#pragma unroll(full)
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for(char y=0; y<SPLIT1; y++)
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{
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sline(0, y)[39] = rbuff[y];
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cline(0, y)[39] = cbuff[y];
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}
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}
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// Scroll bottom two sections
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void scrollLeft1(void)
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{
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for(char x=0; x<39; x++)
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{
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#pragma unroll(full)
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for(char y=SPLIT1; y<SPLIT2; y++)
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{
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sline(0, y)[x] = sline(1, y)[x];
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cline(0, y)[x] = cline(1, y)[x];
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}
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}
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#pragma unroll(full)
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for(char y=SPLIT1; y<SPLIT2; y++)
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{
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sline(0, y)[39] = rbuff[y];
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cline(0, y)[39] = cbuff[y];
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}
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for(char x=0; x<39; x++)
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{
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#pragma unroll(full)
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for(char y=SPLIT2; y<25; y++)
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{
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sline(0, y)[x] = sline(1, y)[x];
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cline(0, y)[x] = cline(1, y)[x];
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}
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}
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#pragma unroll(full)
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for(char y=SPLIT2; y<25; y++)
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{
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sline(0, y)[39] = rbuff[y];
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cline(0, y)[39] = cbuff[y];
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}
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}
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// Prepare a new column with random data
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void prepcol(void)
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{
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for(char i=0; i<25; i++)
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{
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unsigned r = rand();
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cbuff[i] = r & 15;
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rbuff[i] = (r & 16) ? 102 : 160;
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}
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}
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int main(void)
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{
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// Clear the screen
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memset(screen, 0x20, 1000);
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memset(color, 7, 1000);
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vic.color_back = VCOL_BLACK;
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vic.color_border = VCOL_BLACK;
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char x = 0;
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for(;;)
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{
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// Advance one pixel
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x = (x + 1) & 7;
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// If we will cross the character boundary, scroll the top section
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if (x == 0)
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{
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// Wait for raster reaching bottom of first section
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vic_waitLine(50 + 8 * SPLIT1);
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// Scroll first section
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scrollLeft0();
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}
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// Wait for bottom of screen
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vic_waitBottom();
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// Update the pixel offset
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vic.ctrl2 = (7 - x) & 7;
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if (x == 0)
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{
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// Scroll the bottom section if needed
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scrollLeft1();
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}
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else
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{
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// Update the new column somewhere in the middle of the character
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if (x == 4)
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prepcol();
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vic_waitTop();
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}
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}
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return 0;
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}
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