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• iPhone+Quartz+OpenGL. What is the correct way for Quartz and OpenGL to play nice together regarding

  - by dugla

  So we know the CoreGraphics/Quartz imaging model is based on pre-multiplied alpha. We also know that OpenGL blending is based on un-premultiplied alpha. What is the best practice to avoid head explosion when doing blending with textures that are derived from pre-multiplied alpha imagery (PNG files generated in Photoshop with pre-multiplied alpha). Given the apples/oranges mish mash of Quartz and OpenGL, what is the correct glBlendFunc for doing the fundamental Porter/Duff "over" operation? Typical example: A simple paint program. Brush shapes are texture-map patterns created from pre-multiplied alpha rgba images. Paint color is specified via glColor4(...) with the alpha channel used to control paint transparency. GL_MODULATE is used so the brush texture multiplies the (translucent) paint color to blend the color into the canvas. Problem: The texture is premult. The color is not. What is the correct way to handle this fundamental inconsistency? Thanks, Doug

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• OpenGL extensions available on different Android devices

  - by MH114

  I'm in the process of writing an OpenGL ES powered framework for my next Android game(s). Currently I'm supporting three different techniques of drawing sprites: the basic way: using vertex arrays (slow) using vertex-buffer-objects (VBOs) (faster) using the draw_texture extension (fastest, but only for basic sprites, i.e. no transforming) Vertex arrays are supported in OpenGL ES 1.0 and thus in every Android-device. I'm guessing most (if not all) of the current devices also support VBOs and draw_texture. Instead of guessing, I'd like to know the extensions supported by different devices. If majority of devices support VBOs, I could simplify my code and focus only on VBOs + draw_texture. It'd be helpful to know what different devices support, so if you have an Android-device, do report the extensions list please. :) String extensions = gl.glGetString(GL10.GL_EXTENSIONS); I've got a HTC Hero, so I can share those extensions next.

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• Android: Deciding between SurfaceView and OpenGL (GLSurfaceView)

  - by Rich

  Is there a way to decide up front based on the expected complexity of a game/app in the planning phase whether to use regular Canvas drawing in a SurfaceView or to go with OpenGL? I've been playing around with a Canvas and only need 2D movement, and on a fairly new phone I'm getting pretty decent performance with a bunch of primitive objects and a few bitmaps running around the screen on a solid background. Is it fair to say that if I'm going to be drawing background images and increasing the number of objects being moved and drawn on top of them that I should go straight to OpenGL?

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• Screen capture of MDI app with OpenGL graphics using MFC

  - by NPVN

  In our MDI application - which is written in MFC - we have a function to save a screenshot of the MDI client area to file. We are currently doing a BitBlt from the screen into a bitmap, which is then saved. The problem is that some of the MDI child windows have their content rendered by OpenGL, and in the destination bitmap these areas show up as blank or garbled. I have considered some alternatives: - Extract the OpenGL content directly (using glReadPixels), and draw this to the relevant portions of the screen bitmap. - Simulate an ALT+PrtScr, since doing this manually seems to get the content just fine. This will trash the clipboard content, though. - Try working with the DWM. Appart from Vista and Win7, this also needs to work on Win2000 and XP, so this probably isn't the way to go. Any input will be appreciated!

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• OpenGL ES displaying HUD display Text can't be colored black on top of textured 3D objects

  - by ivanceras

  This is a follow-up of this question on here http://iphonedevelopment.blogspot.com/2010/02/drawing-hud-display-in-opengl-es.html It tackles on the HUD (heads up display) which is based on this tutorial http://stackoverflow.com/questions/2681102/opengl-es-displaying-hud-display-has-no-color-on-top-of-textured-3d-objects I wanted to set the "Text" in color BLACK, but it is more complicated than what I thought. Setting it to some other color other than black "glColor4f(0.0, 0.0, 0.0, 1.0);" is just fine. I assume that the culprit must be in the Blending function "glBlendFunc (GL_ONE, GL_ONE);" I experimented a lot of combinations with no luck. Has anyone experimented on this one on top of textured 3D in the backgrounds working?

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• Frame skipping with OpenGL and WinAPI?

  - by user146780

  Here is my situation. I'm creating a drawing application using OpenGL and WinAPI. My OpenGL frame has scrollbars which renders the screen and modifies GlTranslatef when it gets a scroll message. The problem is wen I get too many shapes the scrollbar is less responsive since it cannot rerender it each and every time it gets a scroll message. How could I make it so the scrollbar has priority. I want it to skip drawing if it would compromise the smoothness of the scrolling. I thought of doing rendering on a separate thread but I was told all UI things should stay on the same thread. Thanks

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• xCode screensaver with openGL

  - by moka

  Hi, I am currently simply trying to build a simple screen saver in xcode 3.2 on osx 10.6.3 using an openGL view as described in this article: http://cocoadevcentral.com/articles/000089.php anyways even if I use the exact same code from the example all I see when testing the screen saver is a black screen. I looked in OSX Console if it tells me anything useful. the only thing I get is something like this: [0x0-0x1e01e].com.apple.systempreferences[629] System Preferences(629,0x7fff71071be0) malloc: reference count underflow for 0x20057be80, break on auto_refcount_underflow_error to debug. System Preferences[629] invalid context I have no idea what is wrong, so I would be glad if someone could tell me how to use openGL together with the screensaver template in xCode 3.2. Also, is there a way to make another target so I can preview the screensaver from within xCode? Thanks!

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• OpenGL - lighting of vertices outside clip range

  - by hmp

  I have a problem with lighting in my OpenGL application. When one of the vertices of a drawn polygon goes outside the front clip plane (or has z<0, I'm not sure which), the polygon stops being lighted properly. This however happens on only one machine I tested, with Intel GMA950 card. On nVidia and ATI cards everything looks fine. I guess I am breaking some OpenGL rule here? How should I deal with it? I'd try dividing the scene into smaller polygons, but I'm not sure if it guarantees the case is eliminated (all polygons stepping outside the clipping range are offscreen).

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• Modifying an image with OpenGL ?

  - by chmike

  I have a device to acquire XRay images. Due to some technical constrains, the detector is made of heterogeneous pixel size and multiple tilted and partially overlapping tiles. The image is thus distorted. The detector geometry is known precisely. I need a function converting these distorted images into a flat image with homogeneous pixel size. I have already done this by CPU, but I would like to give a try with OpenGL to use the GPU in a portable way. I have no experience with OpenGL programming, and most of the information I could find on the web was useless for this use. How should I proceed ? How do I do this ? Image size are 560x860 pixels and we have batches of 720 images to process. I'm on Ubuntu.

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• iPhone OpenGL Template is cheating?

  - by carrots

  XCode's OpenGL template seems to be cheating to solve this "stretched" viewport problem I've been trying to understand for the last 3 hours. In the iphone "OpenGL ES Application" template, the colorful square that bounces up and down on the screen is not really a square at all! ES1Renderer.m (the ES2 file as well) static const GLfloat squareVertices[] = { -0.5f, -0.33f, 0.5f, -0.33f, -0.5f, 0.33f, 0.5f, 0.33f, }; But it comes out looking square on the device/simulator due to the stretching/squashing effect of a non-square viewport. I tried to fix it by fiddling with glFrustumf() but that doesn't seem to change the aspect ratio. I was able to get things looking good (not-stretched) when I fed glViewport() with a 1:1 widht:height.. But this doesn't seem like the answer because it offsets the viewport placement. What's the right way to correct for this stretching and why doesn't XCode do it that way?

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• Python OpenGL Can't Redraw Scene

  - by RobbR

  I'm getting started with OpenGL and shaders using GLUT and PyOpenGL. I can draw a basic scene but for some reason I can't get it to update. E.g. any changes I make during idle(), display(), or reshape() are not reflected. Here are the methods: def display(self): glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT ) glMatrixMode(GL_MODELVIEW) glLoadIdentity() glUseProgram(self.shader_program) self.m_vbo.bind() glEnableClientState( GL_VERTEX_ARRAY ) glVertexPointerf(self.m_vbo) glDrawArrays(GL_TRIANGLES, 0, len(self.m_vbo)) glutSwapBuffers() glutReportErrors() def idle(self): test_change += .1 self.m_vbo = vbo.VBO( array([ [ test_change, 1, 0 ], # triangle [ -1,-1, 0 ], [ 1,-1, 0 ], [ 2,-1, 0 ], # square [ 4,-1, 0 ], [ 4, 1, 0 ], [ 2,-1, 0 ], [ 4, 1, 0 ], [ 2, 1, 0 ], ],'f') ) glutPostRedisplay() def begin(self): glutInit() glutInitWindowSize(400, 400) glutCreateWindow("Simple OpenGL") glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB) glutDisplayFunc(self.display) glutReshapeFunc(self.reshape) glutMouseFunc(self.mouse) glutMotionFunc(self.motion) glutIdleFunc(self.idle) self.define_shaders() glutMainLoop() I'd like to implement a time step in idle() but even basic changes to the vertices or tranlastions and rotations on the MODELVIEW matrix don't display. It just puts up the initial state and does not update. Am I missing something?

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• Trouble shooting openGL text textures not showing up correctly cross platform

  - by Michael Minerva

  I have been tasked with solving a problem that is outside of my domain of knowledge and I was hoping I could get some troubleshooting advice from someone more experienced with openGL (I have very little experience with openGL). We are working on a cross platform application that is implemented in a common lisp implementation called ccl. In this application we have a need to display some 3D objects that display text. On the mac, all of the text displays fine but on the PC instead of displaying the text it displays some other texture. At first I thought that maybe the wrong texture was just being referenced so I tried changing the texture number but none of the textures in the list appeared to be the text (or if it was the texture was distorted and did not look like text). I know this problem is very vague and I am not looking for someone to post a solution, but I was wondering if people could suggest places I might look to try and get a handle on this issue.

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• Drawing NGons with OpenGL

  - by user146780

  Is OpenGL, given a series of points, able to fill in a polygon or is this only possible by creating lots of trianges? Thanks

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• OpenGL game written in C with a Cocoa front-end I want to port to Windows

  - by Philip

  Hello, I'm wondering if someone could offer me some tips on how to go about this. I have a MacOS X OpenGL game that is written in very portable C with the exception of the non-game-play GUI. So in Cocoa I set up the window and OpenGL context, manage preferences, registration, listen for keystrokes etc. But all of the drawing and processing of input is handled in nice portable C. So I want to port to Windows. I figured the obvious way to go about was to use the Win32 api. Then I started to read a primer on Win32 and began to wonder if maybe life isn't too short. Can I do this in C# (without converting the backend to C#)? I'd rather devote the time to learning C# than Win32. Any suggestions would be most welcome. I really don't know a lick about Windows. The last version I regularly used was 3.1...

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• I just don't get why there is a glMatrixMode in OpenGL

  - by René Nyffenegger

  I just don't understand what OpenGL's glMatrixMode is for. As far as I can see, when glMatrixMode(GL_MODELVIEW) is called, it is followed by glVertex, glTranslate, glRotate and the like, that is, OpenGL commands that place some objects somewhere in the space. On the other hand, if glOrtho or glFrustum or gluProjection is called (ie how the placed objects are rendered), it has a preceeding call of glMatrixMode(GL_PROJECTION). I guess what I have written so far is an assumption on which someone will prove me wrong, but is not the point of using different *Matrix Mode*s exactly because there are different kinds of gl-functions: those concerned with placing objects and those with how the objects are rendered? So, if someone could shed some light on this issue, I'd certainly appreciate it.

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• iPad + OpenGL ES2. Why the Puzzling Virtual Memory Spike During Device Reorientation?

  - by dugla

  I've been spending the afternoon starring at Xcode Instruments memory monitor trying to decipher the following memory issue. I have a fullscreen OpenGL ES2 app running on iPad. I am fanatical about memory issues so my retains/releases are all nicely balanced. I closely monitor memory leaks. My app is basically squeeky clean. Except occassionally when I reorient the device. Portrait to Landscape. Back and forth I rock the device stress testing my discarding and rebuilding of the OpenGL framebuffer. The ambient memory footprint of my app is about 70MB Real Mems and 180MB Virtual Mems. Real memory hardly varies at all during device rotations. However the virtual mems reading sometimes briefly spikes up to 250MB and then recedes back to 180MB. No real pattern. But clearly related discarding/rebuilding the framebuffer. I see random memory warnings in my NSlogs but the app just hums along, no worries. 1) Since iPhone OS devices don't have VM could someone explain to me what the VM reading actually means? 2) My app totally leak free and generally bulletproof dispite the VM spikes. Never crashes. Rock solid. Should I be concerned about this? 3) There is clearly something happening in OpenGL framebuffer land that is causing this but I am using the API in the proper way: paraphrasing: Discarding the framebuffer: glDeleteRenderbuffers(1, &m_colorbuffer); glDeleteFramebuffers(1, &m_framebuffer); Rebuilding the framebuffer: glGenFramebuffers(1, &m_framebuffer); glGenRenderbuffers(1, &m_colorbuffer); Is there some other memory flushing trick I have missed? Thanks for any insight. Cheers, Doug

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• How to properly use glDiscardFramebufferEXT

  - by Rafael Spring

  This question relates to the OpenGL ES 2.0 Extension EXT_discard_framebuffer. It is unclear to me which cases justify the use of this extension. If I call glDiscardFramebufferEXT() and it puts the specified attachable images in an undefined state this means that either: - I don't care about the content anymore since it has been used with glReadPixels() already, - I don't care about the content anymore since it has been used with glCopyTexSubImage() already, - I shouldn't have made the render in the first place. Clearly, only the 1st two cases make sense or are there other cases in which glDiscardFramebufferEXT() is useful? If yes, which are these cases?

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• glFramebufferTexture2D performance

  - by nornagon

  I'm doing heavy computation using the GPU, which involves a lot of render-to-texture operations. It's an iterative computation, so there's a lot of rendering to a texture, then rendering that texture to another texture, then rendering the second texture back to the first texture and so on, passing the texture through a shader each time. My question is: is it better to have a separate FBO for each texture I want to render into, or should I rather have one FBO and bind the target texture using glFramebufferTexture2D each time I want to change render target? My platform is OpenGL ES 2.0 on the iPhone.

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• How to merge two FBOs?

  - by DevDevDev

  OK so I have 4 buffers, 3 FBOs and a render buffer. Let me explain. I have a view FBO, which will store the scene before I render it to the render buffer. I have a background buffer, which contains the background of the scene. I have a user buffer, which the user manipulates. When the user makes some action I draw to the user buffer, using some blending. Then to redraw the whole scene what I want to do is clear the view buffer, draw the background buffer to the view buffer, change the blending, then draw the user buffer to the view buffer. Finally render the view buffer to the render buffer. However I can't figure out how to draw a FBO to another FBO. What I want to do is essentially merge and blend two FBOs, but I can't figure out how! I'm very new to OpenGL ES, so thanks for all the help.

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• Le Khronos Group publie les spécifications de OpenGL 3.3 et 4.0

  Le Khronos Group publie les spécifications de OpenGL 3.3 et 4.0 Déjà deux ans après la sortie d'OpenGl 3.x, le Khronos Group nous offre le même jour les spécifications des nouvelles versions d'OpenGL : La version 3.3 et la version 4.0 Pour ces nouvelles versions la séparation Core et Compatibility demeurent et, nouveauté pour le GLSL, les versions ont dorénavant le même nom que la version de l'API sous laquelle elles ont été sortis. On nous promet aussi une version 4.0 optimisée, moins dépendante du CPU, notamment concernant la tesselation... N'étant pas familier a OpenGL je n'oserais en dire plus pour les plus curieux voici le lien :

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• Tutoriel OpenGL Moderne : shaders de base, apprenez à utiliser des objets transparents dans vos scènes en OpenGL 3 et supérieur

  Bonjour à tous,La rubrique 2D/3D/Jeux est heureuse de vous présenter une la suite de la série de tutoriels consacrée à OpenGL moderne (les versions à partir d'OpenGL 3.3). Ces tutoriels vous permettront d'intégrer facilement les nouveaux concepts d'OpenGL afin de profiter au maximum des dernières technologies de vos cartes graphiques. Ce dixième tutoriel vous apprendra à mettre en place la transparance dans vos applications OpenGL.Bonne lecture.

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• Tutoriel OpenGL Moderne : texte 2D, affichez des textes en 2D dans votre application OpenGL 3 et supérieur

  Bonjour à tous,La rubrique 2D/3D/Jeux est heureuse de vous présenter une la suite de la série de tutoriels consacrée à OpenGL moderne (les versions à partir d'OpenGL 3.3). Ces tutoriels vous permettront d'intégrer facilement les nouveaux concepts d'OpenGL afin de profiter au maximum des dernières technologies de vos cartes graphiques. Ce onzième tutoriel vous apprendra à afficher du texte en 2D dans vos applications OpenGL.Bonne lecture.

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• Tutoriel OpenGL Moderne : billboards, incrustez des éléments 3D dans votre monde 3D en OpenGL 3 et supérieur

  Bonjour à tous,La rubrique 2D/3D/Jeux est heureuse de vous présenter la suite de la série de tutoriels consacrée à OpenGL moderne (les versions à partir d'OpenGL 3.3). Ces tutoriels vous permettront d'intégrer facilement les nouveaux concepts d'OpenGL afin de profiter au maximum des dernières technologies de vos cartes graphiques. Ce dix-huitième tutoriel vous expliquera comment afficher des billboards (des éléments 2D incrustés dans un monde 3D) en OpenGL.Bonne lecture.Voir aussiToutes les ressources...

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• Cannot get 3D OpenGL support in Vmware guests, how can I fix this?

  - by jjapol

  I have been working at this problem for 2 days now. I cannot for the life of me enable 3D support in VMWare 9 guests. My specifications are: Hardware: Dell Latitude E5520 laptop. Processor: Intel i7-2620M CPU @ 2.70GHz × 4. Memory: 8GB. Video: Intel Sandybridge Mobile x86/MMX/SSE2 OS: Ubuntu 12.04.1 LTS, 32 bit. Vmware Workstation: 9.0.1 build-894247 Glxgears functions fine. Frame rate is ~60fps. Vmware guest: Windows 7 Starting the Windows 7 guest in VMware throws the following errors: No 3D support is available from the host. and Hardware graphics acceleration is not available. I've read through this VMware forum thread, but again the hardware in the post is different (nVidia). I've followed the instructions at this Ask Ubuntu post as closely as possible as the question is nearly the same as mine although my hardware is different. Answer 1 regarding setting mks.gl.allowBlacklistedDrivers = TRUE; in my vmx configuration file causes the VM to crash when it starts. The second answer I followed as closely as possible. I uninstalled VMware, Did sudo apt-get install build-essential linux-headers-$(uname -r) at a terminal, Added the PPA https://launchpad.net/~glasen/+archive/intel-driver, Then at a terminal did sudo apt-get update && sudo apt-get upgrade -y I reinstalled VMware and have the same results: no 3D in guests. I'm getting the feeling that something is awry with the Sandy Bridge driver, but I can't seem to come up with any solutions. Has anyone out there run across this problem also? By the way, the operation of the likes of Solidworks and AutoCad within a Windpws 7 guest does appear to be improved in VMware 9 vs VMware 8 in spite of the fact that 3D support is lacking in the Windows 7 guest. I'd also add that my glxinfo file was nearly identical to the glxinfo file posted at askubuntu.com/questions/181829/…. I had a total of seven minor differences per a comparison using Meld. –

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• How do I render only part of a texture to a point sprite in OpenGL ES for Android?

  - by nbolton

  Using the libgdx framework, I've figured out how to render a texture to a point sprite. The problem is, it renders the entire texture to the point sprite, where I only want a small part of it (since it's an isometric tile image). Here's a snippet from some demo code I wrote... create() { renderer = new ImmediateModeRenderer(); tiles = Gdx.graphics.newTexture( Gdx.files.internal("data/tiles2.png"), TextureFilter.MipMap, TextureFilter.Linear, TextureWrap.ClampToEdge, TextureWrap.ClampToEdge); Gdx.gl.glClearColor(0.6f, 0.7f, 0.9f, 1); Gdx.gl.glEnable(GL10.GL_TEXTURE_2D); Gdx.gl.glEnable(GL11.GL_POINT_SPRITE_OES); Gdx.gl11.glTexEnvi( GL11.GL_POINT_SPRITE_OES, GL11.GL_COORD_REPLACE_OES, GL11.GL_TRUE); Gdx.gl10.glPointSize(s); tiles.bind(); } render() { Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT); renderer.begin(GL10.GL_POINTS); // render 3 point sprites at various 3d points renderer.vertex(-.1f, 0, -.1f); renderer.vertex(0, 0, 0); renderer.vertex(.1f, 0, .1f); // ... more vertices here if needed (one for each sprite) ... renderer.end(); }

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