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POHow to make fading-to-black effect with OpenGL?
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copied!<p>Im trying to achieve fade-to-black effect, but i dont know how to do it. I tried several things but they fail due to how opengl works</p> <p>I will explain how it would work:</p> <p>If i draw 1 white pixel and move it around each frame for one pixel to some direction, each frame the screen pixels will get one R/G/B value less (of range 0-255), thus after 255 frames the white pixel will be fully black. So if i move the white pixel around, i would see a gradient trail going from white to black evenly 1 color value difference compared to previous pixel color.</p> <p><strong>Edit:</strong> I would prefer to know non-shader way of doing this, but if its not possible then i can accept shader-way too.</p> <p><strong>Edit2:</strong> Since there is some confusion around here, I would like to tell that i can do this kind of effect already by drawing a black transparent quad over my whole scene. BUT, this does not work as i want it to work; there is a limit on the darkness the pixels can get, so it will always leave some of the pixels "visible" (above zero color value) because: 1*0.9 = 0.9 -> rounded to 1 again, etc. I can "fix" this by making the trail shorter, but i want to be able to adjust the trail lenght as much as possible and instead of bilinear (if thats the right word) interpolation i want linear (so it would always reduce -1 from each r,g,b value in 0-255 scale, instead of using a percent value).</p> <p><strong>Edit3:</strong> Still some confusion left, so lets be clear: i want to improve the effect that is done by disabling GL_COLOR_BUFFER_BIT from glClear(), i dont want to see the pixels on my screen FOREVER, so i want to make them darker in time, by drawing a quad over my scene that will reduce each of the pixels color value by 1 (in 0-255 scale).</p> <p><strong>Edit4:</strong> I'll make it simple, i want OpenGL method for this, the effect should use as little power, memory or bandwidth as possible. this effect is supposed to work without clearing the screen pixels, so if i draw a transparent quad over my scene, the previous pixels drawn will get darker etc. But as explained above few times, its not working very well. The big NO's are: 1) reading pixels from screen, modifying them one by one in a for loop and then uploading back. 2) rendering my objects X times with different darknesses to emulate the trail effect. 3) multiplying the color values is not an option since it wont make the pixels into black, they will stay on the screen forever at certain brightness (see explanation somewhere above). </p>

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