ARGB32 to YUV12 利用 SDL1.2 SDL_ttf 在视频表面输出文本

提示:ARGB alpha通道的A + 原YUV表面的y0 + 要写进去的y1 = 计算出新的y2.
计算公式为 ( y1 * a + y0 * ( 255 - a ) ) / 255

void  rgb2yuv(int r, int g, int b, int *y, int *u, int *v)
{
	int y0, u0, v0;
	
	y0 =  66*r + 129*g +  25*b;
	u0 = -38*r + -74*g + 112*b;
	v0 = 112*r + -94*g + -18*b;
	
	y0 = (y0+128)>>8;
	u0 = (u0+128)>>8;
	v0 = (v0+128)>>8;
	
	*y = y0 + 16;
	*u = u0 + 128;
	*v = v0 + 128;
}

void  yuv2rgb(int y, int u, int v, int *r, int *g, int *b)
{
	int r0,g0,b0;
	v = v - 128;
	u = u - 128;
	r0 = y + v + (v>>2) + (v>>3) + (v>>5);
	g0 = y - ((u>>2) + (u>>4) + (u>>5)) - ((v>>1) + (v>>3) + (v>>4) + (v>>5));
	b0 = y + u + (u>>1) + (u>>2) + (u>>6);
	
	*r = r0 > 255 ? 255: r0;
	*g = g0 > 255 ? 255: g0;
	*b = b0 > 255 ? 255: b0;
}

int blitSurface2YUV(SDL_Surface *src, SDL_Overlay *dst, SDL_Rect *dstrect ,int isBlended)
{
	Uint8 r, g, b,a;
	int y0,u0,v0;
	int y1,u1,v1;
	int y2,u2,v2;
	int y,x;
	int height = src->h < dstrect->h ? src->h: dstrect->h;
	int width =  src->w < dstrect->w ? src->w: dstrect->w;
	int uv_off = 0;
	Uint32 pixel;
	
	printf ("src->format->BitsPerPixel %d src->format %08X\r\n",src->format->BitsPerPixel,src->format);
	
	if(dst->format != SDL_YV12_OVERLAY)return 1;
	
	for(y = 0; y < height; ++y)
	{
		for(x = 0; x < width; ++x)
		{
			switch(src->format->BitsPerPixel)
			{
			case 8:
				pixel = *((Uint8*)src->pixels + y*src->pitch + x);
				break;
			case 16:
				pixel = *((Uint16*)src->pixels + y*src->pitch/2 + x);
				break;
			case 32:
				pixel = *((Uint32*)src->pixels + y*src->pitch/4 + x);
				
				break;
			default:
				return -1;
			}
			
			//SDL_GetRGB(pixel, src->format, &r, &g, &b);
			SDL_GetRGBA(pixel, src->format, &r, &g, &b,&a);
			
			rgb2yuv(r, g, b, &y1, &u1, &v1);
	  
			if(isBlended)
			{
				y0 = (dst->pixels[0][ (dstrect->y + y) * dst->pitches[0] + (dstrect->x + x)]);
				v0 = (dst->pixels[1][ (uv_off + dstrect->y /2) * dst->pitches[1] + (dstrect->x/2 + x/2)]);
				u0 = (dst->pixels[2][ (uv_off + dstrect->y /2) * dst->pitches[2] + (dstrect->x/2 + x/2)]);
				
				y2 = (Uint8)(( y1 * a + y0 * ( 255 - a ) ) / 255);
				u2 = (Uint8)(( u1 * a + u0 * ( 255 - a ) ) / 255);
				v2 = (Uint8)(( v1 * a + v0 * ( 255 - a ) ) / 255);
				
				y1=y2;
				u1=u2;
				v1=v2;
			}
			
			memset(dst->pixels[0] + (dstrect->y + y) * dst->pitches[0] + (dstrect->x + x), 
				(Uint8)y1  , 1);
			
			if((x%2 == 0 ) && (y%2 == 0 ))
			{
				memset(dst->pixels[1] + (uv_off + dstrect->y /2) * dst->pitches[1] + (dstrect->x/2 + x/2), 
					(Uint8)v1, 1);
				memset(dst->pixels[2] + (uv_off + dstrect->y /2) * dst->pitches[2] + (dstrect->x/2 + x/2), 
					(Uint8)u1, 1);
			}
		}
		if(y%2 == 0)++uv_off;
	}
	return 0;
}