GLDRAWARRAYSINSTANCE(3G)

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version 1.1 · 7 versions
, in centos-stream 9

✨ GLDRAWARRAYSINSTANCE(3G) ✨

okay so this is the GLDRAWARRAYSINSTANCE(3G) manual page, bestie, and the main character function is glDrawArraysInstancedBaseInstance 💅

🌸 NAME 🌸

glDrawArraysInstancedBaseInstance — draw multiple instances of a range of elements with offset applied to instanced attributes. periodt.

🛠️ C SPECIFICATION 🛠️

void glDrawArraysInstancedBaseInstance(GLenum mode, GLint first,
                                       GLsizei count, GLsizei primcount,
                                       GLuint baseinstance);

🎀 PARAMETERS 🎀

  • mode — specifies what kind of primitives to render. the accepted symbolic constants are GL_POINTS, GL_LINE_STRIP, GL_LINE_LOOP, GL_LINES, GL_TRIANGLE_STRIP, GL_TRIANGLE_FAN, GL_TRIANGLES GL_LINES_ADJACENCY, GL_LINE_STRIP_ADJACENCY, GL_TRIANGLES_ADJACENCY, GL_TRIANGLE_STRIP_ADJACENCY and GL_PATCHES ✨
  • first — specifies the starting index in the enabled arrays.
  • count — specifies the number of indices to be rendered.
  • primcount — specifies the number of instances of the specified range of indices to be rendered.
  • baseinstance — specifies the base instance for use in fetching instanced vertex attributes.

🦋 DESCRIPTION 🦋

okay so here’s the tea: glDrawArraysInstancedBaseInstance behaves identically to glDrawArrays() except that primcount instances of the range of elements are executed and the value of the internal counter instanceID advances for each iteration. instanceID is an internal 32-bit integer counter that may be read by a vertex shader as gl_InstanceID 🫶

glDrawArraysInstancedBaseInstance has the same effect as:

if ( mode or count is invalid )
    generate appropriate error
else {
    for (int i = 0; i < primcount ; i++) {
        instanceID = i;
        glDrawArrays(mode, first, count);
    }
    instanceID = 0;
}

specific vertex attributes may be classified as instanced through the use of glVertexAttribDivisor(). Instanced vertex attributes supply per-instance vertex data to the vertex shader. The index of the vertex fetched from the enabled instanced vertex attribute arrays is calculated as: gl _ InstanceID divisor + baseInstance. Note that baseinstance does not affect the shader-visible value of gl_InstanceID 👑

💀 ERRORS 💀

  • GL_INVALID_ENUM is generated if mode is not one of the accepted values.
  • GL_INVALID_OPERATION is generated if a geometry shader is active and mode is incompatible with the input primitive type of the geometry shader in the currently installed program object.
  • GL_INVALID_VALUE is generated if count or primcount are negative.
  • GL_INVALID_OPERATION is generated if a non-zero buffer object name is bound to an enabled array and the buffer object's data store is currently mapped.
no cap, those last two GL_INVALID_OPERATION girlies are separate situations — don’t merge them in your head, bestie 💅

👑 VERSION SUPPORT 👑

vibe check on versions: the function/feature name is glDrawArraysInstancedBaseInstance, and here’s the OpenGL Version support grid translated into bullet form so it stays terminal-friendly 🌈

  • glDrawArraysInstancedBaseInstance — 2.0: -; 2.1: -; 3.0: -; 3.1: -; 3.2: -; 3.3: -; 4.0: -; 4.1: -; 4.2: ✔; 4.3: ✔; 4.4: ✔; 4.5: ✔

🔥 SEE ALSO 🔥

  • glDrawArrays()
  • glDrawElementsInstanced()

Copyright © 2011-2014 Khronos Group. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1.0, 8 June 1999. http://opencontent.org/openpub/.

Copyright © 2011-2014 Khronos Group

signing off with source/version [FIXME: source], date 08/09/2021, and the manual tag GLDRAWARRAYSINSTANCE(3G) 🫶💖✨

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