レイヤ合成(1)

<レイヤ ...>
<レイヤ 2>
<レイヤ 1>
<背景>
 ↓
[合成結果のイメージ]
 ↓
[ウィンドウ表示用イメージ]

#include "sptk.h"

#define WIDTH  200
#define HEIGHT 230

SPTK_IMAGE *winimg;
SPTK_IMAGE32 *layerimg,*blendimg;
int opacity = 255;

void blend_layer()
{
    int ix,iy,a;
    SPTK_PIX_RGBA *psrc,*pdst;
    
    psrc = layerimg->pixbuf;
    pdst = blendimg->pixbuf;
        
    for(iy = 0; iy < layerimg->h; iy++)
    {
        for(ix = 0; ix < layerimg->w; ix++)
        {
            a = psrc->a * opacity / 255;
        
            pdst->r = (psrc->r - pdst->r) * a / 255 + pdst->r;
            pdst->g = (psrc->g - pdst->g) * a / 255 + pdst->g;
            pdst->b = (psrc->b - pdst->b) * a / 255 + pdst->b;
        
            psrc++;
            pdst++;
        }
    }
}

void draw()
{
    sptk_image32_fill_plaid(blendimg, 0, 0, 200, 200);
    
    blend_layer();

    sptk_image32_blt_image(blendimg, 0, 0, 200, 200, winimg, 0, 0);
    sptk_update(NULL, 0, 0, 200, 200, 5);
}

void bar_handle(SPTK_WIDGET *wg,int type,int pos)
{
    if(opacity != pos)
    {
        opacity = pos;
        draw();
    }
}

int main()
{
    sptk_init("test", WIDTH, HEIGHT);
    
    winimg = sptk_window_get_image();
    
    layerimg = sptk_image32_load_bitmap("alphagrad.bmp");
    if(!layerimg) sptk_errexit("cannot load bitmap file");
    
    blendimg = sptk_image32_create(200, 200);
    
    sptk_image_text(winimg, 5, 210, "OPACITY", -1, 0);
        
    sptk_widget_bar_create(0, 55, 208, 135, 15, 0, 255, 255, bar_handle);
    
    draw();
    
    sptk_run();
    
    sptk_image32_free(layerimg);
    sptk_image32_free(blendimg);

    return 0;
}