![]() ![]() Note that the binding does not take effect until the program is next linked. So, considering the shader above, and assuming p as a handle to our program, we could write in our application the following OpenGL instruction: glBindFragDataLocation(p, 0, "colorOut") name: the name of the shader output variable.colorNumber: the output location to bind the variable to.Void glBindFragDataLocation(GLuint program, GLuint colorNumber, const char *name) In the application we should bind the variable colorOut to output location zero, the default location when not using framebuffer objects, using the following function: In the shader above, the variable colorOut is bound to location 0 (zero) by default. Not very interesting though, it just paints everything red! #version 150Īs with uniform variables and vertex attributes, the output variables of the fragment shader also have a location. The shader below is probably the simplest fragment shader we can write. There may be more than one color output if using framebuffer objects. An application should bind user-defined variables to color outputs. By default an application has a single color output, and its type is a vec4. Regarding outputs, these can range, in number, from 1 to GL_MAX_DRAW_BUFFERS. Note: gl_PrimitiveID is only available in version 4.1. If no geometry shader is present, the value reflects the index of the primitive in the OpenGL draw command. gl_PrimitiveID: This variable is an output of the geometry shader.Note that if face culling is enabled then this value will be the same for all pixels. gl_FrontFacing: tells the orientation of the primitive that originated the pixel.gl_FragCoord: contains the fragments coordinate (xf, yf, zf, wf), where (xf, yf) is the pixels position on the window, zf is the depth, and wf is 1/ wc, where wc is the component of the fragments clip space position.Some built-in variables available in a fragment shader are (for a complete list see the GLSL spec section on Built-in Variables): ![]() The fragment shader, similarly to the vertex shader, only has access to the current pixel and its associated data.Īs in the previous stages the fragment shader has access to all uniforms made available in the application. The fragment shader does not have access to the framebuffer, neither at the current pixel’s position, nor at any other pixel position. However, it can change the pixel’s depth (the Z value). a fragment shader can not choose to write the attributes of other pixel. The shader performs computations based on these attributes and the pixels position. This shader is not optional, unless transform feedback is being used.įragment shaders can access the fragment position, and all the interpolated data computed in the rasterization process. The fragments that were found in the rasterization process, and whose attributes were computed in the interpolation phase, are now fed, one by one, to the fragment shader. A fragment is basically a position on the window (X,Y), a depth value (Z), plus all the interpolated data from previous stages. ![]()
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