Direct State AccessGL 4.5

glClearNamedFramebufferfv

Clears one attachment of a framebuffer to a value of your choice, without glClearColor.

Signature

void glClearNamedFramebufferfv(GLuint framebuffer, GLenum buffer, GLint drawbuffer,
                               const GLfloat *value);

How it works

glClear clears every colour attachment to the same glClearColor. With several targets that is often wrong: weighted blended OIT needs its accumulation buffer cleared to 0 and its revealage buffer to 1. This function clears a single one, chosen by its index in the draw-buffer list, to the value given.

Parameters

framebufferGLuint

The framebuffer, 0 for the window.

bufferGLenum

What to clear.

Common values

GL_COLOR
One colour attachment; value points to 4 floats.
GL_DEPTH
The depth buffer; value points to 1 float, drawbuffer must be 0.
drawbufferGLint

For GL_COLOR, the index in the glNamedFramebufferDrawBuffers list (not the attachment enum).

valueconst GLfloat *

The clear value.

Tips & pitfalls

  • Direct State Access (GL 4.5): the object is passed as a parameter, so nothing needs to be bound and no global state is disturbed.

  • Pick the suffix by the attachment's format: fv for float and normalized formats, uiv for unsigned integer (GL_R32UI), iv for signed integer.

Example

example.cpp
1const float zero[4] = { 0, 0, 0, 0 };
2const float one[4]  = { 1, 1, 1, 1 };
3glClearNamedFramebufferfv(oitFbo, GL_COLOR, 0, zero);  // accumulation
4glClearNamedFramebufferfv(oitFbo, GL_COLOR, 1, one);   // revealage

Related

glClearResets the chosen buffers of the current framebuffer (color, depth, stencil).glClearNamedFramebufferuivClears an unsigned-integer colour attachment (an object-ID buffer, for example) to an integer value.glNamedFramebufferDrawBuffersLists which colour attachments the fragment shader's outputs go to (multiple render targets).glClearColorChooses the color glClear will fill the color buffer with.
Official Khronos documentation