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Search found 234 results on 10 pages for 'glsl'.

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• Instanced drawing with OpenGL ES 2.0

  - by Mårten Wikström

  In short: Is it possible to use the gl_InstanceID built-in variable in OpenGL ES 2.0? And, if so, how? Some more info: I want to draw multiple instances of an object using glDrawArraysInstanced and gl_InstanceID, and I want my application to run on multiple platforms, including iOS. The specification clearly says that these features require…

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• change the color of a vertex in a vertex shader

  - by Soubok

  Is it possible to set the color of a single vertex using a GLSL vertex shader program, in the same way that gl_Position changes the position of a vertex ?

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• Fragment Shader Eye-Space unscaled depth coordinate

  - by Ben Jones

  I'm trying to use the unscaled (true distance from the front clipping plane) distance to objects in my scene in a GLSL fragment shader. The gl_FragCoord.z value is smaller than I expect. In my vertex shader, I just use ftransform() to set gl_Position. I'm seeing values between 2 and 3 when I expect them to be between 15 and 20. How can I get…

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• Shaders with pygtkglext

  - by qba

  Do someone know how to get glsl shaders work in gtk-opengl window? With glut all glCreateProgram etc. functions works, but when I tried to put the same gl code into pygtkglext window, its complaining about NullReference: OpenGL.error.NullFunctionError: Attempt to call an undefined function glCreateProgram, check for bool(glCreateProgram) before…

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• Hidden features of OpenGL

  - by subSeven

  Hello! What are some of the hidden features of OpenGL and GLSL ? Do you know some cool tricks/tips ?

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• Updating Textures on Runtime in OpenSceneGraph

  - by Abhishek Bansal

  I am working on a project in which i am required to capture frames from external device video and render them on openSceneGraph Node. I am also using GLSL shaders. But i dont know how to update textures on runtime. For other uniforms we need to make callbacks but do we also need to make callbacks for samplers in glsl and openSceneGraph ? My…

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• Stuffed Animal In OpenGL

  - by anon

  I have seen metal/plastic/water/fire/... shaders for OpenGL. However, it it possible to render something fur-like, say a stuffed animal / teddy bear in OpenGL (I know this is possible with renderman / ray tracers, but I want to do it in OpenGl). If you have pointers to GLSl shaders for this, please point me in the right direction. Thanks!…

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• How do I get the current color of a fragment?

  - by Mason Wheeler

  I'm trying to wrap my head around shaders in GLSL, and I've found some useful resources and tutorials, but I keep running into a wall for something that ought to be fundamental and trivial: how does my fragment shader retrieve the color of the current fragment? You set the final color by saying gl_FragColor = whatever, but apparently that's…

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• my first shader in WebGL

  - by Diego

  Hello, I am writing my first shader in WebGL. I was wondering if the GLSL language has any way to evaluate if an attribute or a uniform is null. According to the specs it does not support to do something like if (attributeX) { dothis(); } else{ dothat(): } And I think it would be a waste to write a bool attribute for each of these…

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• OpenGL ES 2.0 Rendering with a Texture

  - by Kyle

  The iPhone SDK has an example of using ES 2.0 with a set of (Vertex & Fragment) GLSL shaders to render a varying colored box. Is there an example out there on how to render a simple texture using this API? I basically want to take a quad, and draw a texture onto it. The old ES 1.1 API's don't work at all anymore, so I'm needing a…

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• GPGPU programming with OpenGL ES 2.0

  - by Albus Dumbledore

  I am trying to do some image processing on the GPU, e.g. median, blur, brightness, etc. The general idea is to do something like this framework from GPU Gems 1. I am able to write the GLSL fragment shader for processing the pixels as I've been trying out different things in an effect designer app. I am not sure however how I should do…

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• Why does division yield a vastly different result than multiplication by a fraction in floating points.

  - by Avram

  I understand why floating point numbers can't be compared, and know about the mantissa and exponent binary representation, but I'm no expert and today I came across something I don't get: Namely lets say you have something like: float denominator, numerator, resultone, resulttwo; resultone = numerator / denominator; float buff = 1 /…

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• Shadow volume shader optimization (GLSL)

  - by Soubok

  I wondering if there is a way to optimize this vertex shader. This vertex shader projects (in the light direction) a vertex to the far plane if it is in the shadow. void main(void) { vec3 lightDir = (gl_ModelViewMatrix * gl_Vertex - gl_LightSource[0].position).xyz; // if the vertex is lit if ( dot(lightDir,…

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• Atmospheric scattering OpenGL 3.3

  - by user1419305

  Im currently trying to convert a shader by Sean O'Neil to version 330 so i can try it out in a application im writing. Im having some issues with deprecated functions, so i replaced them, but im almost completely new to glsl, so i probably did a mistake somewhere. Original shaders can be found here:…

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• Block filters using fragment shaders

  - by Nils

  I was following this tutorial using Apple's OpenGL Shader Builder (tool similar to Nvidia's fx composer, but simpler). I could easily apply the filters, but I don't understand if they worked correct (and if so how can I improve the output). For example the blur filter: OpenGL itself does some image…

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• How do I perform an HSL transform on a texture?

  - by Mason Wheeler

  If I have an OpenGL texture, and I need to perform HSL modifications on it before rendering the texture, from what I've heard I need a shader. Problem is, I know nothing about shaders. Does anyone know where I would need to look? I want to write a function where I can pass in a texture and three…

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• In OpenGL vertex shader, gl_Position doesn't get homogenized..

  - by KJ

  Hi everyone, I was expecting gl_Position to automatically get homogenized (divided by w), but it seems not working.. Why do the followings make different results? 1) void main() { vec4 p; ... omitted ... gl_Position = projectionMatrix * p; } 2) ... same as above ... p = projectionMatrix…

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• When should a uniform be used in shader programming?

  - by Phineas

  In a vertex shader, I calculate a vector using only uniforms. Therefore, the outcome of this calculation is the same for all instantiations of the vertex shader. Should I just do this calculation on the CPU and upload it as a uniform? What if I have ten such calculations? If I upload a lot of…

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• How to get pixel information inside a fragment shader?

  - by user697111

  In my fragment shader I can load a texture, then do this: uniform sampler2D tex; void main(void) { vec4 color = texture2D(tex, gl_TexCoord[0].st); gl_FragColor = color; } That sets the current pixel to color value of texture. I can modify these, etc and it works well. But a few…

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• Determining line orientation using vertex shaders

  - by Brett

  Hi, I want to be able to calculate the direction of a line to eye coordinates and store this value for every pixel on the line using a vertex and fragment shader. My idea was to calculate the direction gradient using atan2(Gy/Gx) after a modelview tranformation for each pair of vertices…

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• gl_FragColor and glReadPixels

  - by chun0216

  I am still trying to read pixels from fragment shader and I have some questions. I know that gl_FragColor returns with vec4 meaning RGBA, 4 channels. After that, I am using glReadPixels to read FBO and write it in data GLubyte *pixels = new GLubyte[640*480*4]; glReadPixels(0, 0,…

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• What's the best way to draw a fullscreen quad in OpenGL 3.2?

  - by Phineas

  I'm doing ray casting in the fragment shader. I can think of a couple ways to draw a fullscreen quad for this purpose. Either draw a quad in clip space with the projection matrix set to the identity matrix, or use the geometry shader to turn a point into a triangle strip. The…

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• 2 Shaders using the same vertex data

  - by Fonix

  So im having problems rendering using 2 different shaders. Im currently rendering shapes that represent dice, what i want is if the dice is selected by the user, it draws an outline by drawing the dice completely red and slightly scaled up, then render the proper dice over…

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• how to apply shader to specific object

  - by Andrey

  i have several objects on my scene. i want to apply my shader to one of them only. Environment: OpenGL 2.0, C++, GLUT, GLEW.

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• Using a single texture image unit with multiple sampler uniforms

  - by bcrist

  I am writing a batching system which tracks currently bound textures in order to avoid unnecessary glBindTexture() calls. I'm not sure if I need to keep track of which textures have already been used by a particular batch so that if a texture is used twice, it will be…

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