GLDRAWBUFFER(3G)

💅 NAME

glDrawBuffer, glNamedFramebufferDrawBuffer — bestie, these two literally tell OpenGL which color buffers get the draw, and it's giving "choose your fighter" energy 🎨✨ (this is a page from the 3G manual, btw 🫶)

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🌸 C SPECIFICATION

void glDrawBuffer(GLenum buf);

void glNamedFramebufferDrawBuffer(GLuint framebuffer, GLenum buf);

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🎀 PARAMETERS

• framebuffer — the name of the framebuffer object for the glNamedFramebufferDrawBuffer function. It has to be zero, or the name of a framebuffer object. That's the whole vibe check, no cap.
• buf — ok so for the default framebuffer, this argument picks up to four color buffers to draw into. The accepted symbolic constants are GL_NONE, GL_FRONT_LEFT, GL_FRONT_RIGHT, GL_BACK_LEFT, GL_BACK_RIGHT, GL_FRONT, GL_BACK, GL_LEFT, GL_RIGHT, and GL_FRONT_AND_BACK. The initial value is GL_FRONT for single-buffered contexts and GL_BACK for double-buffered contexts. For framebuffer objects, the GL_COLOR_ATTACHMENT$m$ and GL_NONE enums are accepted, where $m$ is a value between 0 and GL_MAX_COLOR_ATTACHMENTS. 💖

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✨ DESCRIPTION ✨

So when colors get written to the frame buffer, they go into the color buffers that glDrawBuffer specifies. Periodt. For the default framebuffer you can use one of these values 👇

• GL_NONE — no color buffers are written. absolutely nothing. silence. 💀
• GL_FRONT_LEFT — only the front left color buffer is written.
• GL_FRONT_RIGHT — only the front right color buffer is written.
• GL_BACK_LEFT — only the back left color buffer is written.
• GL_BACK_RIGHT — only the back right color buffer is written.
• GL_FRONT — only the front left and front right color buffers are written. If there's no front right color buffer, only the front left color buffer is written.
• GL_BACK — only the back left and back right color buffers are written. If there's no back right color buffer, only the back left color buffer is written.
• GL_LEFT — only the front left and back left color buffers are written. If there's no back left color buffer, only the front left color buffer is written.
• GL_RIGHT — only the front right and back right color buffers are written. If there's no back right color buffer, only the front right color buffer is written.
• GL_FRONT_AND_BACK — all the front and back color buffers (front left, front right, back left, back right) are written. If there are no back color buffers, only the front left and front right color buffers are written. If there are no right color buffers, only the front left and back left color buffers are written. If there are no right or back color buffers, only the front left color buffer is written. the way it just keeps narrowing down 😭

Lowkey important: if more than one color buffer is selected for drawing, then blending or logical operations are computed and applied independently for each color buffer, and they can produce different results in each buffer. so like, don't assume they'll match, bestie 🙈

Monoscopic contexts include only left buffers, and stereoscopic contexts include both left and right buffers. Likewise, single-buffered contexts include only front buffers, and double-buffered contexts include both front and back buffers. The context is selected at GL initialization — not your call, it's already decided 🌈

For framebuffer objects, the GL_COLOR_ATTACHMENT$m$ and GL_NONE enums are accepted, where $m$ is a value between 0 and GL_MAX_COLOR_ATTACHMENTS. And heads up 👑: glDrawBuffer will set the draw buffer for fragment colors other than zero to GL_NONE.

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💀 ERRORS

• GL_INVALID_OPERATION is generated by glNamedFramebufferDrawBuffer if framebuffer is not zero or the name of an existing framebuffer object. not a real one? rejected. 🚫
• GL_INVALID_ENUM is generated if buf is not an accepted value.
• GL_INVALID_OPERATION is generated if the default framebuffer is affected and none of the buffers indicated by buf exists. 😭
• GL_INVALID_OPERATION is generated if a framebuffer object is affected and buf is not equal to GL_NONE or GL_COLOR_ATTACHMENT$m$, where $m$ is a value between 0 and GL_MAX_COLOR_ATTACHMENTS.

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🔍 ASSOCIATED GETS

glGet() with argument GL_DRAW_BUFFER — that's your vibe check tool right there 🫶

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👑 VERSION SUPPORT

ok so the chart is literally a wall of checkmarks, here's the tea ☕ The OpenGL versions covered are 2.0, 2.1, 3.0, 3.1, 3.2, 3.3, 4.0, 4.1, 4.2, 4.3, 4.4, and 4.5, and the rows are the function names ✨

• glDrawBuffer — ✔ in 2.0, ✔ in 2.1, ✔ in 3.0, ✔ in 3.1, ✔ in 3.2, ✔ in 3.3, ✔ in 4.0, ✔ in 4.1, ✔ in 4.2, ✔ in 4.3, ✔ in 4.4, ✔ in 4.5. she ate every single one 💅
• glNamedFramebufferDrawBuffer — - in 2.0, - in 2.1, - in 3.0, - in 3.1, - in 3.2, - in 3.3, - in 4.0, - in 4.1, - in 4.2, - in 4.3, - in 4.4, and ✔ in 4.5. she's a 4.5 exclusive, main character energy only 🌟

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🦋 SEE ALSO

glBlendFunc(), glColorMask(), glDrawBuffers(), glLogicOp(), glReadBuffer() — go read those too, iykyk 📚

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🍓 COPYRIGHT

Copyright © 1991-2006 Silicon Graphics, Inc. Copyright © 2010-2014 Khronos Group. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.

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💜 COPYRIGHT (the sequel, yes it's literally listed again)

Copyright © 1991-2006 Silicon Graphics, Inc. Copyright © 2010-2014 Khronos Group

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and that's the whole page, bestie 🎀 source is [FIXME: source] and the date on this bad boy is 08/09/2021, from the GLDRAWBUFFER(3G) manual — mwah, drink water, and go draw into the right buffer 💖✨🦋