//设置半透明
void Sprite::SetAlpha( int alpha )
{
if( m_spr )
{
SDL_gfxSetAlpha( m_spr, alpha );
}
}
void Draw(SDL_Surface *screen)
{
int rate,x,y,s;
SDL_Rect dest,clip;
SDL_Surface *texture_image;
SDL_Surface *texture_target1;
SDL_Surface *texture_target2;
FPSmanager fpsm;
Uint32 rmask, gmask, bmask, amask;
int width_half = screen->w/2;
int height_half = screen->h/2;
Uint32 text_color = 0xffffffff;
/* Define masks for 32bit surface */
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
rmask = 0xff000000;
gmask = 0x00ff0000;
bmask = 0x0000ff00;
amask = 0x000000ff;
#else
rmask = 0x000000ff;
gmask = 0x0000ff00;
bmask = 0x00ff0000;
amask = 0xff000000;
#endif
/* Create semi-transparent textured surface */
s=64;
texture_image = SDL_DisplayFormatAlpha(SDL_CreateRGBSurface(SDL_SWSURFACE, s, s, 32, rmask, gmask, bmask, amask));
/* Add some color */
boxRGBA(texture_image, 0, 0, s/2, s/2, 255, 0, 0, 255);
boxRGBA(texture_image, s/2, 0, s, s/2, 0, 255, 0, 255);
boxRGBA(texture_image, 0, s/2, s/2, s, 0, 0, 255, 255);
boxRGBA(texture_image, s/2, s/2, s, s, 255, 255, 255, 255);
/* Make 75%-transparent */
SDL_gfxSetAlpha(texture_image, 96);
/* Set alpha channel use to per-pixel blending */
SDL_SetAlpha(texture_image, SDL_SRCALPHA, 255);
/* Create an all transparent surface */
texture_target1 = SDL_DisplayFormatAlpha(SDL_CreateRGBSurface(SDL_SWSURFACE, 256, 256, 32, rmask, gmask, bmask, amask));
/* Make 75%-transparent */
SDL_gfxSetAlpha(texture_target1, 64);
/* Set alpha channel use to per-pixel blending */
SDL_SetAlpha(texture_target1, SDL_SRCALPHA, 255);
/* Create an all transparent surface (2) */
texture_target2 = SDL_DisplayFormatAlpha(SDL_CreateRGBSurface(SDL_SWSURFACE, 256, 256, 32, rmask, gmask, bmask, amask));
/* Make 75%-transparent */
SDL_gfxSetAlpha(texture_target2, 64);
/* Set alpha channel use to per-pixel blending */
SDL_SetAlpha(texture_target2, SDL_SRCALPHA, 255);
/* Define clipping region for left box */
clip.x = width_half-256-10 ;
clip.y = height_half-256/2 ;
clip.w = 256;
clip.h = 256;
/* Initialize Framerate manager */
SDL_initFramerate(&fpsm);
/* Set/switch framerate */
rate=5;
SDL_setFramerate(&fpsm,rate);
/* --- Drawing loop */
while (1) {
/* Event handler */
HandleEvent();
/* Black screen */
ClearScreen(screen);
/* Random position of new texture */
x=(rand() % (256+2*s))-s;
y=(rand() % (256+2*s))-s;
/* Same for comparison texture */
dest.x = x;
dest.y = y;
dest.w = texture_image->w;
dest.h = texture_image->h;
SDL_BlitSurface(texture_image, NULL, texture_target1, &dest);
/* Blit image into the target using custom Blit function. */
dest.x = x;
dest.y = y;
dest.w = texture_image->w;
dest.h = texture_image->h;
SDL_gfxBlitRGBA(texture_image, NULL, texture_target2, &dest);
/* Draw comparison target on screen (left) */
dest.x = width_half-256-10;
dest.y = height_half-256/2;
dest.w = 256;
dest.h = 256;
SDL_BlitSurface(texture_target1, NULL, screen, &dest);
/* Draw combiner target on screen (right) */
dest.x = width_half+10;
dest.y = height_half-256/2;
dest.w = 256;
dest.h = 256;
SDL_BlitSurface(texture_target2, NULL, screen, &dest);
/* Draw some frames with titles */
rectangleColor(screen, width_half-256-10-1, height_half-256/2-1, width_half-256-10-1+257, height_half-256/2-1+257, text_color);
rectangleColor(screen, width_half+10-1, height_half-256/2-1, width_half+10-1+257, height_half-256/2-1+257, text_color);
stringColor(screen, width_half-256-10-1, height_half-256/2-1-36, " SDL Standard Blitter ", text_color);
stringColor(screen, width_half-256-10-1, height_half-256/2-1-24, "Image --sdlBlit--> Target1", text_color);
stringColor(screen, width_half-256-10-1, height_half-256/2-1-12, "Target1 --sdlBlit--> Screen", text_color);
stringColor(screen, width_half+10-1, height_half-256/2-1-36, " SDL_gfx Compositing Blitter", text_color);
stringColor(screen, width_half+10-1, height_half-256/2-1-24, "Image --gfxBlit--> Target2", text_color);
stringColor(screen, width_half+10-1, height_half-256/2-1-12, "Target2 --sdlBlit--> Screen", text_color);
stringColor(screen, width_half-256-10-1, height_half-256/2-1-60, "gfxBlitRGBA Demo: Target1/2 A=64 (25%), Image A=96 (37%)", text_color);
/* Display by flipping screens */
SDL_Flip(screen);
/* Delay to fix rate */
SDL_framerateDelay(&fpsm);
}
}
