Re: [9fans] Porter-Duff alpha blending

[andrey mirtchovski]

just for fun, the attached file should run the whole gamut of
allocimage chan options in the 32-bit range (with RGB24 thrown in for
good measure) and will create files in /tmp for each possible
combination without involving drawing to the screen display (ideally
this should be done in memdraw, i suppose).

i think page will display them honestly, but i'm not sure. i'll leave
to you to convert the resulting images for outside viewing :)

#include <u.h>
#include <libc.h>
#include <draw.h>
#include <cursor.h>

Image *col;
Image *back;

ulong types[] = {
                RGBA32, 
                ARGB32, 
                XRGB32,
                XBGR32,
                RGB24,
};
char *descs[] = {
        "rgba32",
        "argb32",
        "xrgb32",
        "xbgr32",
        "rgb24",
};

void
main(void) {
        int fd, i, j, k;
        char *str;
        ulong type = RGBA32;

        if(initdraw(nil, nil, "tri") < 0)
                exits("initdraw");

        for(j = 0; j < 5; j++) {
                for(k = 0; k < 5; k++) {
                        str= smprint("/tmp/%s-over-%s.1", descs[k], descs[j]);
                        print("creating: %s\n", str);
                        back = allocimage(display, Rect(0, 0, 800, 300), 
types[j], 0, DBlack);

                        for(i = 0; i < 0xff; i++) {
                                col = allocimage(display, Rect(0,0,1,1), 
types[k], 1, setalpha(DWhite, 0xff-i));
                                draw(back, Rect(0,i,200,i+1), col, nil, ZP);
                                freeimage(col);
                                col = allocimage(display, Rect(0,0,1,1), 
types[k], 1, setalpha(DRed, 0xff-i));
                                draw(back, Rect(200,i,400,i+1), col, nil, ZP);
                                freeimage(col);
                                col = allocimage(display, Rect(0,0,1,1), 
types[k], 1, setalpha(DGreen, 0xff-i));
                                draw(back, Rect(400,i,600,i+1), col, nil, ZP);
                                freeimage(col);
                                col = allocimage(display, Rect(0,0,1,1), 
types[k], 1, setalpha(DBlue, 0xff-i));
                                draw(back, Rect(600,i,800,i+1), col, nil, ZP);
                                freeimage(col);

                        }

                        fd = create(str, OWRITE, 0664);
                        if(fd < 0)
                                sysfatal("create");
                        writeimage(fd, back, 0);
                        close(fd);
                }
        }
}