51 lines
912 B
C
51 lines
912 B
C
#include <lib/display.h>
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void dreverse(int x, int y, int width, int height)
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{
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int vram_offset_y;
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int j;
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// Check error.
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if (width < 0 || height < 0)
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return;
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// Get "real" X position and area width.
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if (x < 0)
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{
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width = width + x;
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x = 0;
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} else {
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if (x + width >= DISPLAY_SCREEN_WIDTH)
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width = DISPLAY_SCREEN_WIDTH - x;
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}
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// Get "real" Y position and area height.
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if (y < 0)
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{
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height = height + x;
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y = 0;
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} else {
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if (y + height >= DISPLAY_SCREEN_HEIGHT)
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height = DISPLAY_SCREEN_HEIGHT - x;
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}
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// Check potential error.
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// @note we do not check height because the while()
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// while do the job for us.
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if (width < 0)
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return;
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// Generate VRAM offset for Y axis.
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vram_offset_y = (y + height - 1) << 4;
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while (--height >= 0)
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{
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j = width + x;
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while (--j >= x)
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{
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vram[(j >> 3) + vram_offset_y] ^= 0x80 >> (j & 7);
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}
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vram_offset_y = vram_offset_y - 16;
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}
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}
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