glsl

After calling glVertexAttribPointer(GLuint index, ...) the vertex attribute is disabled by default as the docs say By default, all client-side capabilities are disabled, including all generic vertex attribute arrays. Why must we enable it using an extra function? Can someone name a case, where this is useful? When researching I learned the following: By using the layout(location = x) qualifier in GLSL or glBindAttribLocation we can set the location explicitly rather then letting OpenGL generate it. But this is not the point of my question. glEnableVertexAttribArray can not be used to draw one

I'm trying to render a freetype font using OpenGL, following the example posted at http://en.wikibooks.org/wiki/OpenGL_Programming/Modern_OpenGL_Tutorial_Text_Rendering_02 . I've been able to generate a texture atlas from the font, creating shaders and creating quads. What I seem to get stuck at is passing the texture to the shader and/or getting the correct UVs for my quads. Been struggling for a good while now and really need the help. The following is the struct I use to create my texture atlas. struct FontCharacter { float advanceX; float advanceY; float bitmapWidth; float bitmapHeight;

I'm starting out on using OpenGL with Qt, and with Shaders (I have OpenGL experience, but not with shaders yet) I'm following this tutorial: http://releases.qt-project.org/learning/developerguides/qtopengltutorial/OpenGLTutorial.pdf (the official Qt5 OpenGL tutorial). The problem is, that when I try to run my program, I get a black screen and the following error messages: QGLShader::compile(Vertex): ERROR: 0:1: '' : version '130' is not supported QGLShader::compile(Fragment): ERROR: 0:1: '' : version '130' is not supported My program is based on a QGLWidget With some browsing on the interwebs

If you want to render an imposter geometry (say like a sphere ), then the standard practice is to draw it using two triangles (say by passing one vertex and making a triangle strip with a geometry shader). This is nice because it allows the extent of the billboard to be set fairly simply: you compute the actual world space positions directly. Geometry shaders can alternately output point primitives, and I don't see a reason why they shouldn't. The only issue is finding some way to scale gl_PointSize so that you get that effect. The only precedent I could find were this question (whose answer I

In a simple hello-world OpenGL program, which simply draws a static triangle on the window, when I set the 3 vertex of the triangle to red, green and blue color, the triangle is filled with gradient. But when I use shaders like this: Vertex Shader: attribute vec4 aVertex; attribute vec4 aColor; varying vec4 vColor; void main(void) { gl_Position = gl_ModelViewMatrix * gl_ProjectionMatrix * aVertex; vColor = aColor; } where the attributes aVertex and aColor comes from a vertex buffer, passed through a call of glVertexAttribPointer . Fragment Shader: varying vec4 vColor; void main(void) { gl

I've just upgraded my MacBook Pro to Mavericks (MacOS 10.9), including Xcode. According to Apple's "OpenGL Capabilities Table", this version has support for OpenGL 4.1, but a call to glGetString(GL_VERSION) returns "1.2" and my GLSL 3.30 shader, which begins with "#version 330" refuses to load, saying that version is not supported. Do I need to do something to Mavericks to enable 4.1 support? When you request your pixel format using one of the lower-level APIs on OS X, you need to add the following to your attribute list in order to use a core profile: CGL: kCGLPFAOpenGLProfile,