The model, view and projection matrices are three separate matrices. Model maps from an object’s local coordinate space into world space, view from world space to camera space, projection from camera to screen. If you compose all three, you can use the one result to map all the way from object space to screen space, … Read more
“Vertex Array Object” is brought to you by the OpenGL ARB Subcommittee for Silly Names. Think of it as a geometry object. (As an old time SGI Performer programmer, I call them geosets.) The instance variables/members of the object are your vertex pointer, normal pointer, color pointer, attrib N pointer, … When a VAO is … Read more
The identity matrix, in terms of the projection and modelview matrices, essentially resets the matrix back to its default state. As you hopefully know, glTranslate and glRotate are always relative to the matrix’s current state. So for instance, if you call glTranslate, you are translating from the matrix’s current ‘position’, not from the origin. But … Read more
All About OpenGL Objects The standard model for OpenGL objects is as follows. Objects have state. Think of them as a struct. So you might have an object defined like this: struct Object { int count; float opacity; char *name; }; The object has certain values stored in it and it has state. OpenGL objects … Read more
A fragment shader is the same as pixel shader. One main difference is that a vertex shader can manipulate the attributes of vertices. which are the corner points of your polygons. The fragment shader on the other hand takes care of how the pixels between the vertices look. They are interpolated between the defined vertices … Read more
There’s no official extension in the spec. OpenGL doesn’t handle loading shaders from files; you just pass in the shader code as a string, so there’s no specific file format. However, glslang, Khronos’ reference GLSL compiler/validator, uses the following extensions to determine what type of shader that the file is for: .vert – a vertex … Read more
The Framebuffer object is not actually a buffer, but an aggregator object that contains one or more attachments, which by their turn, are the actual buffers. You can understand the Framebuffer as C structure where every member is a pointer to a buffer. Without any attachment, a Framebuffer object has very low footprint. Now each … Read more
Rendering outlines, unless you render only a dozen characters total, remains a “no go” due to the number of vertices needed per character to approximate curvature. Though there have been approaches to evaluate bezier curves in the pixel shader instead, these suffer from not being easily antialiased, which is trivial using a distance-map-textured quad, and … Read more
You can’t easily communicate back to the CPU from within GLSL. Using glslDevil or other tools is your best bet. A printf would require trying to get back to the CPU from the GPU running the GLSL code. Instead, you can try pushing ahead to the display. Instead of trying to output text, output something … Read more
glPolygonMode( GL_FRONT_AND_BACK, GL_LINE ); to switch on, glPolygonMode( GL_FRONT_AND_BACK, GL_FILL ); to go back to normal. Note that things like texture-mapping and lighting will still be applied to the wireframe lines if they’re enabled, which can look weird.