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POAlpha/texturing issues in an OpenGL wrapper
 

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  1. POAlpha/texturing issues in an OpenGL wrapper
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    <p>I'm in the process of writing a wrapper for some OpenGL functions. The goal is to wrap the context used by the game Neverwinter Nights, in order to apply post-processing shader effects. After learning OpenGL (this is my first attempt to use it) and much playing with DLLs and redirection, I have a somewhat working system. </p> <p>However, when the post-processing fullscreen quad is active, all texturing and transparency drawn by the game are lost. This shouldn't be possible, because all my functions take effect after the game has completely finished its own rendering.</p> <p>The code does not use renderbuffers or framebuffers (both refused to compile on my system in any way, with or with GLEW or GLee, despite being supported and usable by other programs). Eventually, I put together this code to handle copying the texture from the buffer and rendering a fullscreen quad:</p> <pre><code>extern "C" SEND BOOL WINAPI hook_wglSwapLayerBuffers(HDC h, UINT v) { if ( frameCount &gt; 250 ) { frameCount++; if ( frameCount == 750 ) frameCount = 0; if ( nwshader-&gt;thisframe == NULL ) { createTextures(); } glBindTexture(GL_TEXTURE_2D, nwshader-&gt;thisframe); glCopyTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 0, 0, nwshader-&gt;width, nwshader-&gt;height, 0); glClearColor(0.0f, 0.5f, 0.0f, 0.5f); glClear(GL_COLOR_BUFFER_BIT); glEnable(GL_TEXTURE_2D); glDisable(GL_DEPTH_TEST); glBlendFunc(GL_ONE, GL_ZERO); glEnable(GL_BLEND); glMatrixMode(GL_PROJECTION); glPushMatrix(); glLoadIdentity(); glOrtho( 0, nwshader-&gt;width , nwshader-&gt;height , 0, -1, 1 ); glMatrixMode(GL_MODELVIEW); glPushMatrix(); glLoadIdentity(); glColor4f(1.0f, 1.0f, 1.0f, 1.0f); glBegin(GL_POLYGON); glTexCoord2f(0.0f, 1.0f); glVertex2d(0, 0); glTexCoord2f(0.0f, 0.0f); glVertex2d(0, nwshader-&gt;height); glTexCoord2f(1.0f, 0.0f); glVertex2d(nwshader-&gt;width, nwshader-&gt;height); glTexCoord2f(1.0f, 1.0f); glVertex2d(nwshader-&gt;width, 0); glEnd(); glMatrixMode( GL_PROJECTION ); glPopMatrix(); glMatrixMode( GL_MODELVIEW ); glPopMatrix(); glEnable(GL_DEPTH_TEST); glDisable(GL_TEXTURE_2D); glBindTexture(GL_TEXTURE_2D, 0); } else { frameCount++; } if ( h == grabbedDevice ) { Log-&gt;logline("Swapping buffer on cached device."); } return wglSwapLayerBuffers(h,v); } </code></pre> <p>This code functions almost functions perfectly and has no notable slow-down. However, when it is active (I added the frameCount condition to turn it on and off every ~5 seconds), all alpha and texturing are completely ignored by the game renderer. I'm not turning off any kind of blending or texturing before this function (the only OpenGL calls are to create the nwshader->thisframe texture). I was able to catch a few screenshots of what's happening:</p> <p>Broken A: <a href="http://i4.photobucket.com/albums/y145/peachykeen000/outside_brokenA.png" rel="nofollow noreferrer">http://i4.photobucket.com/albums/y145/peachykeen000/outside_brokenA.png</a> <br> Broken B: <a href="http://i4.photobucket.com/albums/y145/peachykeen000/outside_brokenB.png" rel="nofollow noreferrer">http://i4.photobucket.com/albums/y145/peachykeen000/outside_brokenB.png</a> <br> (note, in B, the smoke in the back is not broken, it is correctly transparent. So is the HUD.) <br> Broken Interior: <a href="http://i4.photobucket.com/albums/y145/peachykeen000/transparency_broken.png" rel="nofollow noreferrer">http://i4.photobucket.com/albums/y145/peachykeen000/transparency_broken.png</a> <br> Correct Interior (for comparison): <a href="http://i4.photobucket.com/albums/y145/peachykeen000/transparency_proper.png" rel="nofollow noreferrer">http://i4.photobucket.com/albums/y145/peachykeen000/transparency_proper.png</a> <br></p> <p>The drawing of the quad also breaks menus, turning the whole thing into a black surface with a single white box. I suspect it is a problem with either depth or how the game is drawing certain objects, or a state that is not being reset properly. I've used GLintercept to dump a full log of all calls in a frame, and didn't see anything wrong (the call to wglSwapLayerBuffers is always last).</p> <p>Being brand new to working with OpenGL, I really have no clue what's going wrong (or how to fix it) and nothing I've tried has helped. What am I missing?</p>
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    1. COTry to narrow down the line of your code that's causing the problem (by removing them one by one). I bet it's going to be `createTextures()`, `glBindTexture` or `glCopyTexImage2D` (but that's just a guess).
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    2. COcreateTextures is a call to one of my functions, which creates the necessary texture if it doesn't exist (used to texture the quad as it's rendered). glBindTexture is used, as far as I understand, to tell the quad to use that particular texture for its texturing. Am I mistaken there? And glCopyTexImage2D is to copy the backbuffer into my texture (I know that is working, since I get an overlay with the mis-rendered frame).
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