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POglReadPixels() sets GL_INVALID_OPERATION flag for no reason
 

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  1. POglReadPixels() sets GL_INVALID_OPERATION flag for no reason
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    <p>I'm trying to implement color picking with FBO. I have multisampled FBO (fbo[0]) which I use to render the scene and I have non multisampled FBO (fbo[1]) which I use for color picking.</p> <p>The problem is: when I try to read pixel data from fbo[1] everything goes well until glReadPixels call which sets GL_INVALID_OPERATION flag. I've checked the manual and can't find the reason why.</p> <p>The code to create FBO:</p> <pre><code>glBindRenderbuffer(GL_RENDERBUFFER, rbo[0]); glRenderbufferStorageMultisample(GL_RENDERBUFFER, numSamples, GL_RGBA8, resolution[0], resolution[1]); glBindRenderbuffer(GL_RENDERBUFFER, rbo[1]); glRenderbufferStorageMultisample(GL_RENDERBUFFER, numSamples, GL_DEPTH24_STENCIL8, resolution[0], resolution[1]); glBindRenderbuffer(GL_RENDERBUFFER, rbo[2]); glRenderbufferStorage(GL_RENDERBUFFER, GL_R32UI, resolution[0], resolution[1]); glBindRenderbuffer(GL_RENDERBUFFER, rbo[3]); glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH24_STENCIL8, resolution[0], resolution[1]); glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo[1]); glFramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, rbo[3]); glFramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, rbo[2]); OGLChecker::checkFBO(GL_DRAW_FRAMEBUFFER); glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo[0]); glFramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, rbo[1]); glFramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, rbo[0]); OGLChecker::checkFBO(GL_DRAW_FRAMEBUFFER); </code></pre> <p>My checker stays silent so the FBOs are complete. Next the picking code</p> <pre><code>glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo[1]); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT ); // bla, bla, bla // do the rendering unsigned int result; glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0); glBindFramebuffer(GL_READ_FRAMEBUFFER, fbo[1]); int sb; glReadBuffer(GL_COLOR_ATTACHMENT0); glBindBuffer(GL_PIXEL_PACK_BUFFER, 0); glGetIntegerv(GL_SAMPLE_BUFFERS, &amp;sb); // glBindFramebuffer(GL_READ_FRAMEBUFFER, 0); OGLChecker::getGlError(); std::cerr &lt;&lt; "Sample buffers " &lt;&lt; sb &lt;&lt; std::endl; glReadPixels(pos.x(), resolution.y() - pos.y(), 1, 1, GL_RED, GL_UNSIGNED_INT, &amp;result); OGLChecker::getGlError(); return result; </code></pre> <p>the output:</p> <pre><code>Sample buffers 0 OpenGL Error : Invalid Operation </code></pre> <p>The interesting fact that if I uncomment glBindFramebuffer(GL_READ_FRAMEBUFFER, 0); then no error happens and pixels are read from screen (but I don't need this).</p> <p>What may be wrong here?</p>
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      1. POglReadPixels() sets GL_INVALID_OPERATION flag for no reason
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    1. COAnother interesting fact. If I change RBO's format from GL_R32UI to GL_R32F everything works fine, except I want to store and read integers and don't loose precision on convertion between uint32 and float. (BTW, the output from fragment shader is uvec4)
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      1. POglReadPixels() sets GL_INVALID_OPERATION flag for no reason
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    2. COWell the problem was with format of framebuffer. glReadBuffer() generates error only when I try to read from buffer with integer formats (like GL_RGBA8I or GL_RGBA8UI or GL_R32UI). No problems when reading from GL_RGBA8 or GL_R32F. That may be the fix for the problem if anyone else encounters it.
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      1. POglReadPixels() sets GL_INVALID_OPERATION flag for no reason
      1. USOleg Titov
 

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