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GL/gl.h - OpenGL Graphics API

Category: 📂 gl/ (Graphics & Display) Header: <GL/gl.h> Scope: OpenGL 1.1+ (Legacy/Core)

The GL/gl.h header provides the interface for OpenGL, a cross-platform API for rendering 2D and 3D vector graphics. It interacts with the GPU driver to perform hardware-accelerated rendering.

Facilities Overview

Facility Category Key Symbols Description
State Control glClear, glClearColor, glEnable Configuring the global rendering state.
Drawing glDrawArrays, glDrawElements Initiating rendering commands from buffers.
Buffers glGenBuffers, glBindBuffer Managing GPU-side memory (VBOs).
View System glViewport Mapping Normalized Device Coordinates to window pixels.

Types & Variables

GLuint

typedef unsigned int GLuint;

Standard unsigned 32-bit integer.

GLint

typedef int GLint;

Standard signed 32-bit integer.

GLfloat

typedef float GLfloat;

Standard 32-bit floating point.

GLenum

typedef unsigned int GLenum;

Enumerated type for OpenGL constants (e.g., GL_FLOAT, GL_TRIANGLES).

Functions

State Control

glClearColor

void glClearColor(GLfloat red, GLfloat green, GLfloat blue, GLfloat alpha)

Specifies the red, green, blue, and alpha values used by glClear to clear the color buffers. Values are clamped to [0, 1].

Returns: None.

Example 
#include <GL/gl.h>

void setup_render(void) {
    // Set clear color to teal
    glClearColor(0.0f, 0.5f, 0.5f, 1.0f);
}

glClear

void glClear(GLbitfield mask)

Sets the bitplane area of the window to values previously selected by glClearColor, glClearDepth, and glClearStencil.

  • mask: Bitwise OR of GL_COLOR_BUFFER_BIT, GL_DEPTH_BUFFER_BIT, etc.

Returns: None.

Buffer Management

glGenBuffers

void glGenBuffers(GLsizei n, GLuint *buffers)

Generates n buffer object names (IDs). No buffer objects are associated with the returned names until they are first bound.

Returns: None.

glBindBuffer

void glBindBuffer(GLenum target, GLuint buffer)

Binds a named buffer object to the specified buffer binding point (target).

  • target: GL_ARRAY_BUFFER (Vertex attributes), GL_ELEMENT_ARRAY_BUFFER (Indices), etc.

Returns: None.

glBufferData

void glBufferData(GLenum target, GLsizeiptr size, const void *data, GLenum usage)

Creates and initializes a buffer object's data store.

  • usage: GL_STATIC_DRAW, GL_DYNAMIC_DRAW, etc.

Returns: None.

Example 
#include <GL/gl.h>

void upload_triangle(GLuint vbo) {
    float vertices[] = {
        -0.5f, -0.5f, 0.0f,
         0.5f, -0.5f, 0.0f,
         0.0f,  0.5f, 0.0f
    };
    
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
}

Drawing

glDrawArrays

void glDrawArrays(GLenum mode, GLint first, GLsizei count)

Render primitives from array data.

  • mode: GL_TRIANGLES, GL_LINES, etc.

Returns: None.

glViewport

void glViewport(GLint x, GLint y, GLsizei width, GLsizei height)

Specifies the affine transformation of x and y from normalized device coordinates to window coordinates.

Returns: None.