81 lines
2.2 KiB
C
81 lines
2.2 KiB
C
/* Example of direct pixel access with SDL. */
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#include <SDL/SDL.h>
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#include <stdio.h>
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#include <stdlib.h>
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Uint16 CreateHicolorPixel(SDL_PixelFormat * fmt, Uint8 red,
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Uint8 green, Uint8 blue)
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{
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Uint16 value;
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/* This series of bit shifts uses the information from the SDL_Format structure
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* to correctly compose a 16-bit pixel value from 8-bit red, green, and blue data
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*/
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value = ((red >> fmt->Rloss) << fmt->Rshift) +
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((green >> fmt->Gloss) << fmt->Gshift) +
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((blue >> fmt->Bloss) << fmt->Bshift);
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return value;
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}
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int main()
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{
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SDL_Surface *screen;
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Uint16 *raw_pixels;
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int x, y;
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/* Initialize SDL's video system and check for errors. */
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if (SDL_Init(SDL_INIT_VIDEO) != 0) {
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printf("Unable to initialize SDL: %s\n", SDL_GetError());
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return 1;
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}
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atexit(SDL_Quit);
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/* Attempt to set a 256x256 hicolor */
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screen = SDL_SetVideoMode(256, 256, 16, 0);
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if (screen == NULL) {
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printf("Unable to set video mode: %s\n", SDL_GetError());
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return 1;
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}
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/* Video memory can be strange, and it's sometimes necessary
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* to "lock it before it can be modified, SDL abstracts this
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* with the SDL_LockSurface function. */
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SDL_LockSurface(screen);
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/* Get a pointer to the video surface's memory. */
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raw_pixels = (Uint16 *) screen->pixels;
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/* We can now safely write to the video surface. We'll draw
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* a nice gradient patern by varying our red and blue components
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* along the X and Y axes. Notice the forumula used to calculate
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* the offset into the framebuffer for each pixel.
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* (The pitch is the number of bytes per scanline in memory.) */
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for (x=0; x < 256; x++) {
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for (y=0; y < 256; y++) {
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Uint16 pixel_color;
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int offset;
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pixel_color = CreateHicolorPixel(screen->format,
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x, 0, y);
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offset = (screen->pitch /2 * y + x);
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raw_pixels[offset] = pixel_color;
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}
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}
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/* We're finished drawing, so unlock the surface. */
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SDL_UnlockSurface(screen);
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/* Inform SDL that the screen has been chnaged. This is
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* necessary because SDL's screen surface is not always the real
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* framebuffer; it is sometimes emulated behind the scenes. */
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SDL_UpdateRect(screen, 0, 0, 0, 0);
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/* Pause for a few seconds as the viewer gasps in awe. */
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SDL_Delay(3000);
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return 0;
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}
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