alpha-sdl.c

Linux游戏编程源码

/* Example of alpha blending with SDL. */

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

int main()
{
    SDL_Surface *screen;
    SDL_Surface *background;
    SDL_Surface *image_with_alpha;
    SDL_Surface *image_without_alpha;
    SDL_Rect src, dest;

    /* 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 320x200 hicolor (16-bit) video mode. */
    screen = SDL_SetVideoMode(320, 200, 16, 0);
    if (screen == NULL) {
	printf("Unable to set video mode: %s\n", SDL_GetError());
	return 1;
    }

    /* Load the bitmap files. The first file was created with
       an alpha channel, and the second was not. Notice that
       we are now using IMG_Load instead of SDL_LoadBMP. */
    image_with_alpha = IMG_Load("with-alpha.png");
    if (image_with_alpha == NULL) {
	printf("Unable to load bitmap.\n");
	return 1;
    }

    image_without_alpha = IMG_Load("without-alpha.png");
    if (image_without_alpha == NULL) {
	printf("Unable to load bitmap.\n");
	return 1;
    }

    background = IMG_Load("background.png");
    if (background == NULL) {
	printf("Unable to load bitmap.\n");
	return 1;
    }

    /* Draw the background. */
    src.x = 0;
    src.y = 0;
    src.w = background->w;
    src.h = background->h;
    dest.x = 0;
    dest.y = 0;
    dest.w = background->w;
    dest.h = background->h;
    SDL_BlitSurface(background, &src, screen, &dest);

    /* Draw the first image, which has an alpha
       channel. We must specifically enable alpha
       blending. */
    SDL_SetAlpha(image_with_alpha, SDL_SRCALPHA, 0);
    src.w = image_with_alpha->w;
    src.h = image_with_alpha->h;
    dest.w = src.w;
    dest.h = src.h;
    dest.x = 40;
    dest.y = 50;
    SDL_BlitSurface(image_with_alpha, &src, screen, &dest);

    /* Draw the second image, which has no alpha
       channel. Instead, we will set a 50% transparency
       factor for the entire surface. */
    SDL_SetAlpha(image_without_alpha, SDL_SRCALPHA, 128);
    src.w = image_without_alpha->w;
    src.h = image_without_alpha->h;
    dest.w = src.w;
    dest.h = src.h;
    dest.x = 180;
    dest.y = 50;
    SDL_BlitSurface(image_without_alpha, &src, screen, &dest);

    /* Ask SDL to update the entire screen. */
    SDL_UpdateRect(screen, 0, 0, 0, 0);

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

    /* Free the memory that was allocated to the bitmaps. */
    SDL_FreeSurface(background);
    SDL_FreeSurface(image_with_alpha);
    SDL_FreeSurface(image_without_alpha);

    return 0;
}