direct-pixel-drawing-sdl.c

Linux游戏编程源码

/* Example of direct pixel access with SDL. */

#include <SDL/SDL.h>
#include <stdio.h>
#include <stdlib.h>

Uint16 CreateHicolorPixel(SDL_PixelFormat * fmt, Uint8 red, Uint8 green,
			  Uint8 blue)
{
    Uint16 value;

    /* This series of bit shifts uses the information from the SDL_Format
       structure to correctly compose a 16-bit pixel value from 8-bit red,
       green, and blue data. */
    value = ((red >> fmt->Rloss) << fmt->Rshift) +
	((green >> fmt->Gloss) << fmt->Gshift) +
	((blue >> fmt->Bloss) << fmt->Bshift);

    return value;
}

int main()
{
    SDL_Surface *screen;
    Uint16 *raw_pixels;
    int x, y;

    /* Initialize SDL's video system and check for errors. */
    if (SDL_Init(SDL_INIT_VIDEO) != 0) {
	printf("Unable to initialize SDL: %s\n", SDL_GetError());
	return 1;
    }

    /* Make sure SDL_Quit gets called when the program exits! */
    atexit(SDL_Quit);

    /* Attempt to set a 256x256 hicolor (16-bit) video mode.
       This will set some type of 16-bit mode, but we won't
       know which particular pixel format ahead of time. If
       the video card can't handle hicolor modes, SDL will
       emulate it. */
    screen = SDL_SetVideoMode(256, 256, 16, 0);
    if (screen == NULL) {
	printf("Unable to set video mode: %s\n", SDL_GetError());
	return 1;
    }

    /* Video memory can be strange, and it's sometimes necessary to
       "lock" it before it can be modified. SDL abstracts this with
       the SDL_LockSurface function. */
    SDL_LockSurface(screen);

    /* Get a pointer to the video surface's memory. */
    raw_pixels = (Uint16 *) screen->pixels;

    /* We can now safely write to the video surface. We'll draw a nice
       gradient pattern by varying our red and blue components along
       the X and Y axes. Notice the formula used to calculate the
       offset into the framebuffer for each pixel.
       (The pitch is the number of bytes per scanline in memory.) */
    for (x = 0; x < 256; x++) {
	for (y = 0; y < 256; y++) {
	    Uint16 pixel_color;
	    int offset;
	    pixel_color = CreateHicolorPixel(screen->format, x, 0, y);
	    offset = (screen->pitch / 2 * y + x);
	    raw_pixels[offset] = pixel_color;
	}
    }

    /* We're finished drawing, so unlock the surface. */
    SDL_UnlockSurface(screen);

    /* Inform SDL that the screen has been changed. This is necessary
       because SDL's screen surface is not always the real framebuffer;
       it is sometimes emulated behind the scenes. */
    SDL_UpdateRect(screen, 0, 0, 0, 0);

    /* Pause for a few seconds as the viewer gasps in awe. */
    SDL_Delay(3000);

    return 0;
}