What is early Z?

Early Fragment Test (sometimes called Early Depth Test) is a feature supported by many GPUs that allow the certain Per-Sample Processing tests that discard fragments to proceed before fragment processing in the rendering pipeline.

What is Gl_depth_test?

To enable depth testing, call glEnable with GL_DEPTH_TEST. When rendering to a framebuffer that has no depth buffer, depth testing always behaves as though the test is disabled. When depth testing is disabled, writes to the depth buffer are also disabled.

What does GL depth test do?

When depth testing is enabled, OpenGL tests the depth value of a fragment against the content of the depth buffer. OpenGL performs a depth test and if this test passes, the fragment is rendered and the depth buffer is updated with the new depth value. If the depth test fails, the fragment is discarded.

What is Z buffer in OpenGL?

A depth buffer, also known as a z-buffer, is a type of data buffer used in computer graphics to represent depth information of objects in 3D space from a particular perspective. Depth buffers are an aid to rendering a scene to ensure that the correct polygons properly occlude other polygons.

What is Z Prepass?

The z-prepass operation is a depth-only render pass that bypasses the fragment shader (except when a surface has an alpha mask), and it processes fragment-bound scenes in about 1/3 the time of a regular shading pass on NVIDIA GPUs, which have special fixed-function support for depth-only rendering.

What does a fragment shader do?

A Fragment Shader is the Shader stage that will process a Fragment generated by the Rasterization into a set of colors and a single depth value. The fragment shader is the OpenGL pipeline stage after a primitive is rasterized. Fragment shaders take a single fragment as input and produce a single fragment as output.

Why does Z fighting happen?

Z-fighting, also called stitching or planefighting, is a phenomenon in 3D rendering that occurs when two or more primitives have very similar distances to the camera. This would cause them to have near-similar or identical values in the z-buffer, which keeps track of depth.

How does Z buffer work?

The Z buffer is a two-dimensional array (X and Y) that stores the Z-value of each screen pixel. If another object must be rendered at the same pixel location, the algorithm overrides the previous value if the new pixel is closer to the camera.

How does the Z buffer algorithm determine which surface are hidden?

Z-buffer, which is also known as the Depth-buffer method is one of the commonly used method for hidden surface detection. It is an Image space method. Image space methods are based on the pixel to be drawn on 2D. For these methods, the running time complexity is the number of pixels times number of objects.

How does z-buffer algorithm determine which surface are hidden?

Is there such thing as an early Z test?

Early Z is not something you can turn on or off through any particular state you set on the device. The hardware will perform z-testing as early as it can and in such a way that you didn’t know it was anywhere other than after the pixel shader.

What’s the purpose of early Z in GameDev.net?

But early-z is supposed to let one do the depth test before the fragments are processed and through that test discard fragments which fail the test. This would give an increased running performance as a fragment shader with a heavy implementation wouldn’t need to be executed as many times.

How to disable early Z test in DirectX 11?

Alpha testing, use of ‘discard’ (killing the pixel) and alpha to coverage will all certainly disable early-z writes as the pixel shaders need to be run before the hardware can determine whether to write a depth value or not.

What do you mean by early Z graphics?

Usually there are three things that are included in the term “early Z”, and they’re all hardware optimisations that you shouldn’t be concerned about too much (except in cases where you might inadvertantly switch them off): Z Compression, Fast Z Clear and Hierarchical Z-Buffer.