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How to access the depth buffer from a fragment shader?
In the fragment shader, this quad samples the depth buffer at that location and changes its color/alpha in order to make that pixel as foggy as needs be. Now I know I can render the scene with the depth buffer linked to a texture, render the scene normally and then render the fog, passing it that texture, but this is one rendering too many.
How to write a shader in rendering 2?
The fundamentals of shader files are explained in Rendering 2, Shader Fundamentals. Give it a read if you’re unfamiliar with writing shaders so you know the basics. The minimum to get a working shader is to define a Shaderblock with a Propertiesblock plus a SubShaderblock with a Passblock inside it.
What is the z component of a fragment shader?
The z component is the depth value that would be used for the fragment’s depth if no shader contained any writes to gl_FragDepth. This is useful for invariance if a shader conditionally computes gl_FragDepth but otherwise wants the fixed functionality fragment depth.
How does the depth buffer work in OpenGL?
I had an idea for fog that I would like to implement in OpenGl: After the scene is rendered, a quad is rendered over the entire viewport. In the fragment shader, this quad samples the depth buffer at that location and changes its color/alpha in order to make that pixel as foggy as needs be.
What are the output variables in fragment shader?
User-defined output variables in the fragment shader can only be the following GLSL types: floats, integers, vectors of the same. They can also be arrays of one of these types, including arrays of arrays (though you are strongly encouraged to avoid this).
What is the depth of a fragment in OpenGL?
This value is the result of the fixed functionality that interpolates primitives after vertex processing to generate fragments. The z component is the depth value that would be used for the fragment’s depth if no shader contained any writes to gl_FragDepth.
How to access the depth of a fragment?
You don’t have to render the whole scene a new, just the fog overlay on top of it. If you want to access only the depth of the newly rendered fragment, just use gl_FragCoord.z, this variable (that should only be read to keep performance) holds the depth buffer value the new fragment will have.
Can a scene be rendered twice to the depth buffer?
Be able to render the scene once, both to the normal depth buffer/screen and to the texture for fog. What’s so wrong with first rendering the scene normally, with depth going into a separate depth texture attachment, then render the fog, finally compositing them.
How to test the depth of a fragment?
When depth testing is active, the depth value from the fragment is compared to the depth value from the matching sample currently in the framebuffer. Let us call the fragment’s depth N, while the framebuffer’s depth P. The conditional test is of the form (N FUNC P), where FUNC is specified by this function:
Why is there an early fragment test in OpenGL?
Early fragment tests, as an optimization, exist to prevent unnecessary executions of the Fragment Shader. If a fragment will be discarded based on the Depth Test (due perhaps to being behind other geometry), it saves performance to avoid executing the fragment shader.