OpenGL Cheatsheet

Basics

Use this OpenGL reference while you build software engineering projects, review code for technical interview prep, or polish examples for a software engineer resume.

Setup and Initialization

OpenGL is a state machine. You set state, then draw; state persists until changed. A context must be created before any GL call — the context owns all GL objects.

// Typical GLFW + GLAD bootstrap
#include <glad/glad.h>
#include <GLFW/glfw3.h>

glfwInit();
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 6);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
// glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // macOS

GLFWwindow* window = glfwCreateWindow(800, 600, "Title", nullptr, nullptr);
glfwMakeContextCurrent(window);   // bind context to this thread

if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) { /* fail */ }

Context Hints (common `glfwWindowHint` values)

Hint	Values	Notes
`GLFW_CONTEXT_VERSION_MAJOR`	3–4	Major GL version
`GLFW_CONTEXT_VERSION_MINOR`	0–6	Minor GL version
`GLFW_OPENGL_PROFILE`	`GLFW_OPENGL_CORE_PROFILE` / `GLFW_OPENGL_COMPAT_PROFILE`	Core removes deprecated APIs
`GLFW_OPENGL_FORWARD_COMPAT`	`GL_TRUE`	Required on macOS
`GLFW_SAMPLES`	0, 2, 4, 8	MSAA sample count
`GLFW_DOUBLEBUFFER`	`GL_TRUE` (default)	Double-buffered swap
`GLFW_RESIZABLE`	`GL_TRUE` / `GL_FALSE`	Window resizable
`GLFW_VISIBLE`	`GL_TRUE` / `GL_FALSE`	Show on creation

The Render Loop

glViewport(0, 0, 800, 600); // map NDC to pixel coords

while (!glfwWindowShouldClose(window)) {
    glfwPollEvents();           // process input events

    glClearColor(0.1f, 0.1f, 0.1f, 1.0f);  // set clear color (RGBA, 0–1)
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

    // --- draw calls here ---

    glfwSwapBuffers(window);    // present back buffer
}

glfwTerminate();

Clear mask bits

Bit	Clears
`GL_COLOR_BUFFER_BIT`	Color buffer to `glClearColor` value
`GL_DEPTH_BUFFER_BIT`	Depth buffer to `glClearDepth` value (default 1.0)
`GL_STENCIL_BUFFER_BIT`	Stencil buffer to `glClearStencil` value (default 0)

Querying Capabilities

GLint maxTexUnits;
glGetIntegerv(GL_MAX_TEXTURE_IMAGE_UNITS, &maxTexUnits);

const GLubyte* vendor   = glGetString(GL_VENDOR);
const GLubyte* renderer = glGetString(GL_RENDERER);
const GLubyte* version  = glGetString(GL_VERSION);
const GLubyte* glsl     = glGetString(GL_SHADING_LANGUAGE_VERSION);

Common `glGetIntegerv` queries

Token	Description
`GL_MAX_TEXTURE_SIZE`	Max 1D/2D texture dimension
`GL_MAX_3D_TEXTURE_SIZE`	Max 3D texture dimension
`GL_MAX_TEXTURE_IMAGE_UNITS`	Max texture units in fragment shader
`GL_MAX_VERTEX_ATTRIBS`	Max vertex attribute slots (≥16)
`GL_MAX_UNIFORM_BLOCK_SIZE`	Max UBO size in bytes
`GL_MAX_SAMPLES`	Max MSAA samples
`GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS`	Across all shader stages

Error Handling

// Poll every error (can be called in a loop)
GLenum err;
while ((err = glGetError()) != GL_NO_ERROR) {
    // err is one of the values below
}

Error codes

Code	Meaning
`GL_NO_ERROR`	No error
`GL_INVALID_ENUM`	Enum argument out of range
`GL_INVALID_VALUE`	Numeric argument out of range
`GL_INVALID_OPERATION`	Invalid operation for current state
`GL_INVALID_FRAMEBUFFER_OPERATION`	Framebuffer not complete
`GL_OUT_OF_MEMORY`	Not enough memory

// GL 4.3+ debug output (preferred over polling)
glEnable(GL_DEBUG_OUTPUT);
glEnable(GL_DEBUG_OUTPUT_SYNCHRONOUS);  // call on the thread that triggered it
glDebugMessageCallback([](GLenum src, GLenum type, GLuint id, GLenum sev,
                          GLsizei len, const GLchar* msg, const void* param) {
    fprintf(stderr, "GL: %s\n", msg);
}, nullptr);
glDebugMessageControl(GL_DONT_CARE, GL_DONT_CARE, GL_DEBUG_SEVERITY_NOTIFICATION,
                      0, nullptr, GL_FALSE); // silence trivial notifications

Enable / Disable Capabilities

glEnable(cap);    // turn on
glDisable(cap);   // turn off
GLboolean b = glIsEnabled(cap);

Common capability tokens

Token	Effect
`GL_DEPTH_TEST`	Fragment depth comparison
`GL_STENCIL_TEST`	Stencil test
`GL_BLEND`	Alpha blending
`GL_CULL_FACE`	Back/front face culling
`GL_SCISSOR_TEST`	Restrict rendering to scissor rect
`GL_MULTISAMPLE`	MSAA (usually on by default)
`GL_LINE_SMOOTH`	Anti-aliased lines (legacy)
`GL_POLYGON_OFFSET_FILL`	Depth offset for filled polys
`GL_PRIMITIVE_RESTART`	Restart index in index buffers
`GL_DEBUG_OUTPUT`	Async debug messages (4.3+)
`GL_FRAMEBUFFER_SRGB`	sRGB-correct writes to sRGB FBOs

Viewport and Scissor

glViewport(x, y, width, height);       // lower-left origin, pixels
glDepthRange(nearVal, farVal);          // NDC Z → window Z (default 0,1)
glScissor(x, y, width, height);        // must also glEnable(GL_SCISSOR_TEST)

Gotcha: after a window resize you must call glViewport again. GLFW does not do it automatically.

Object Naming Pattern

Every GL object follows the same generate / bind / delete lifecycle:

GLuint id;
glGen*(1, &id);    // allocate name (no storage yet)
glBind*(target, id);  // bind → subsequent calls operate on it
// ... configure / upload ...
glDelete*(1, &id); // free GPU resources

This pattern applies to: textures, buffers, VAOs, framebuffers, renderbuffers, samplers, queries, transform-feedback objects, and program pipelines.