<div dir="ltr">Hello, Thanks for your answer.<div> </div><div>Below is a small test program (works on little endian machines).</div><div> </div><div>As is the result is already strange to me :</div><div><div> in: r=20 g=20 b=80 a=FF</div> <div> out: r=90 g=90 b=C0 a=FF</div></div><div>Where as I expected the fill color #FFFFFFFF x the mask 0x80 = #FFFFFF80 and so an output of #9090FFFF.</div><div> </div><div>However, if I set the fill color to #FFFFFF80, the result seems really wrong :</div> <div><div>in: r=20 g=20 b=80 a=FF</div><div>out: r=98 g=98 b=E0 a=FF</div></div><div> </div><div>I would expect fill x mask => #FFFFFF40 and thus out: #606060C0FF.</div><div> </div><div>I especially do not understand how a lower alpha input color can end up in a lighter output on the target image.</div> <div> </div><div>What I am doing wrong here ?</div><div> </div><div>Thanks.</div><div> </div><div> </div><div>#include <stdlib.h> #include <stdio.h> union C { uint32_t value; struct RGBA8888 { uint8_t a; uint8_t b; uint8_t g; uint8_t r; } rgba; }; void testPixmapOps() { // create target image full with r=0x20 g=0x20 b=0x80 a=0xFF size_t w = 100; // multiple of 4 for alignment size_t h = 100; C *target = (C*)malloc(w * h * sizeof(C)); for(size_t i = 0; i < w * h; ++i) target[i].value = 0x202080FF; printf("in: r=%02X g=%02X b=%02X a=%02X\n", target[0].rgba.r, target[0].rgba.g, target[0].rgba.b, target[0].rgba.a); // connect target to pixman image pixman_image_t *ptarget = pixman_image_create_bits(PIXMAN_r8g8b8a8, w, h, (uint32_t*)target, w * sizeof(uint32_t)); // create fill pixman_color_t cfill; cfill.red = uint16_t(0xFF) << 8; cfill.green = uint16_t(0xFF) << 8; cfill.blue = uint16_t(0xFF) << 8; cfill.alpha = uint16_t(0xFF) << 8; pixman_image_t *pfill = pixman_image_create_solid_fill(&cfill); // create mask with a=0x80 uint8_t *mask = (uint8_t*)malloc(w * h); for(size_t i = 0; i < w * h; ++i) mask[i] = 0x80; pixman_image_t *pmask = pixman_image_create_bits(PIXMAN_a8, w, h, (uint32_t*)mask, w); // do compositing pixman_image_composite( PIXMAN_OP_OVER, pfill, pmask, ptarget, // src_x, src_y 0, 0, // mask_x, mask_y 0, 0, // dest_x, dest_y, width, height 0, 0, w, h); // display one pixel of target printf("out: r=%02X g=%02X b=%02X a=%02X\n", target[0].rgba.r, target[0].rgba.g, target[0].rgba.b, target[0].rgba.a); } </div><div> </div><div> </div></div><div class="gmail_extra"> <div class="gmail_quote">2014-06-11 21:49 GMT+02:00 Søren Sandmann <<a href="mailto:soren.sandmann@gmail.com" target="_blank">soren.sandmann@gmail.com</a>>: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="HOEnZb"><div class="h5">Eric Nicolas <<a href="mailto:erik.nicolas@gmail.com">erik.nicolas@gmail.com</a>> writes: > Hello, > > I have a question about the OP modes when compositing with Pixman. I had a look at the source code, but this part of the code is quite complex, so I couldn’t find the answer there. > > What I would like to do is : > - Use a plain color via a pixman_image_create_solid_fill on a RGBA color ; > - Use a PIXMAN_a8 mask ; > - Modify a target PIXMAN_r8g8b8a8 image. > So I do a pixman_image_composite(OP, fill, mask, target, …). > > My problem is that I cannot find an OP which would allow me to blend fill and mask together into target. I mean if ‘fill’ color has an alpha (for instance 0x80), mask is also an alpha (for instance 0x80), I expect the target to be blent with the color modified with an alpha of 0x40 (full fill color x mask alpha => blent to target). > > The closest I found is PIXMAN_OP_ATOP, but it always use the RGB from > the fill color and the A from the mask, it never blends the color with > the mask before compositing onto the target. </div></div>The PIXMAN_OP_OVER operator used with a solid color, a PIXMAN_a8 mask and a PIXMAN_r8g8b8a8 target will multiply the fill color with the pixel from the a8 mask and then blend the result onto the target image. But maybe this is not what you want to do. If not, it might be helpful if you could post images showing what you would like to get, and what you are getting. Søren </blockquote></div> </div>