glClearGLDEPTH

glClearGLDEPTH is not an official OpenGL function. In standard OpenGL, the depth buffer is cleared by calling glClear with the GL_DEPTH_BUFFER_BIT mask, typically as glClear(GL_DEPTH_BUFFER_BIT). The depth buffer stores per-pixel depth values used by the depth test to determine which fragments are visible in the final image.

The depth buffer is associated with the currently bound framebuffer. When a clear is issued for the depth buffer, each pixel in the depth buffer is set to a clear depth value. This value is set by the depth clear state, commonly configured with a function like glClearDepth or its float variant glClearDepthf, and the default depth clear value is 1.0, representing the farthest depth in normalized device coordinates.

Clear operations can target one or multiple buffers. For example, to clear both color and depth buffers in one call, you can use glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT). If you only need to clear depth, you would issue glClear(GL_DEPTH_BUFFER_BIT). Clearing does not enable depth testing by itself; you typically enable depth testing with glEnable(GL_DEPTH_TEST) and configure how depths compare with glDepthFunc. The depth mask, controlled by glDepthMask, determines whether writes to the depth buffer are allowed during rendering.

Common usage patterns involve clearing the depth buffer at the start of each new frame or pass, ensuring a consistent depth baseline for rendering. It is also common to clear color and depth buffers between rendering passes or after resizing a window to reset the framebuffer state.

Notes and pitfalls: the depth buffer must be attached to the currently bound framebuffer, and the depth test should be configured appropriately for correct rendering. Misunderstandings often arise from confusing GL_DEPTH_BUFFER_BIT with other buffer bits or from overlooking that glClear affects the currently bound draw framebuffer.