Notes

gl function names are verb + object, with a type suffix. Call order only matters where one call reads state another call sets.

Reading a function name

Piece	Meaning	Example
glGen*	Allocate several, handles written through a pointer	glGenBuffers(1, &buf)
glCreate*	Allocate one, handle returned	glCreateShader(GL_VERTEX_SHADER)
glBind*	Put an object into a slot	glBindBuffer
gl*Data	Upload into the bound object	glBufferData
glGet*Location	Find a shader variable’s index by name	glGetUniformLocation
glUniform*	Set a uniform on the current program	glUniform1f
glUse*	Pick the active program	glUseProgram
glDraw*	Run the pipeline	glDrawElements
Suffix	Count + type; v = pass a pointer	2i two ints, Matrix3fv

Order: what must come first

First	Then	Why
glUseProgram	glUniform*	Uniforms belong to the current program
glBindBuffer(ARRAY)	glVertexAttribPointer	Pointer wires the buffer bound at that moment
glBindBuffer(ELEMENT_ARRAY)	glDrawElements	Draw reads indices from that slot
All setup	glDrawElements	The draw uses whatever state exists right then
glDrawElements	glDisableVertexAttribArray	Close the input after use

Calls with no dependency can swap freely (Enable vs Pointer, uniforms vs vertex wiring).

Each draw sets up its own state instead of relying on what init left behind, since other code and other objects change bindings in between.

The three counts

glBufferData(
    target,
    BYTES,                  // total bytes: count * sizeof(element)
    ptr,
    usage);

glVertexAttribPointer(
    loc,
    COMPONENTS_PER_VERTEX,  // 3 for vec3
    GL_FLOAT,
    GL_FALSE,
    STRIDE_BYTES,           // 0 = tightly packed
    OFFSET);                // nullptr = start of buffer

glDrawElements(
    GL_TRIANGLES,
    INDEX_COUNT,            // total indices, 3 per triangle
    GL_UNSIGNED_INT,
    nullptr);

glEnableVertexAttribArray is off by default. When off, every vertex reads one constant value instead of the buffer.

Matrix uniform

glUniformMatrix3fv(loc, 1, GL_FALSE, glm::value_ptr(model)); // or &model[0][0]

• 1: number of matrices (arrays of mat3 can take more).
• GL_FALSE: no transpose. glm and GL are both column-major.
• Pointer: GL reads 9 contiguous floats from there.
• T, R, S are multiplied into one matrix on the CPU; the shader multiplies once per vertex.

Related

OpenGL Hub · OpenGL handles and state machine · Matrix composition order (SRT)