OpenGL

Graphique 3D - ENSIMAG 2A

OpenGL Main Concepts

OpenGL defines an API of a rendering system.

Context

Contains all of the information that will be used by the OpenGL system to render

State

OpenGL context information used by the rendering system

Shader

Programmable stage of the rendering pipeline

Object

Group of state values that could be bind to the context

Before Rendering

Create data on CPU

Before Rendering

Generate buffer object name for vertex positions and bind it to the GL_ARRAY_BUFFER target

GLuint posVBO, colVBO, indicesVBO;

glGenBuffer(1, &posVBO);
glBindBuffer(GL_ARRAY_BUFFER, posVBO);









	  

Before Rendering

Create and initialize buffer object's data store of the currently bound buffer object

GLuint posVBO, colVBO, indicesVBO;

glGenBuffer(1, &posVBO);
glBindBuffer(GL_ARRAY_BUFFER, posVBO);
glBufferData(GL_ARRAY_BUFFER, 12*sizeof(float), vPos, GL_STATIC_DRAW);








	  

Before Rendering

Create and initialize buffer object for vertex colors

GLuint posVBO, colVBO, indicesVBO;

glGenBuffer(1, &posVBO);
glBindBuffer(GL_ARRAY_BUFFER, posVBO);
glBufferData(GL_ARRAY_BUFFER, 12*sizeof(float), vPos, GL_STATIC_DRAW);

glGenBuffer(1, &colVBO);
glBindBuffer(GL_ARRAY_BUFFER, colVBO);
glBufferData(GL_ARRAY_BUFFER, 16*sizeof(float), vCol, GL_STATIC_DRAW);




	  

Before Rendering

Create and initialize buffer object for triangle indices

GLuint posVBO, colVBO, indicesVBO;

glGenBuffer(1, &posVBO);
glBindBuffer(GL_ARRAY_BUFFER, posVBO);
glBufferData(GL_ARRAY_BUFFER, 12*sizeof(float), vPos, GL_STATIC_DRAW);

glGenBuffer(1, &colVBO);
glBindBuffer(GL_ARRAY_BUFFER, colVBO);
glBufferData(GL_ARRAY_BUFFER, 16*sizeof(float), vCol, GL_STATIC_DRAW);

glGenBuffer(1, &indicesVBO);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indicesVBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, 6*sizeof(unsigned int), vIndices, GL_STATIC_DRAW);
	  

Vertex Specification

Specify the value of a uniform variables for the program object

int projLoc = glGetUniformLocation(program, "projMat");
int viewlLoc = glGetUniformLocation(program, "viewMat");	      
int modelLoc = glGetUniformLocation(program, "modelMat");

glUniformMatrix4fv(projLoc, 1, GL_FALSE, projMat);
glUniformMatrix4fv(viewlLoc, 1, GL_FALSE, viewMat);
glUniformMatrix4fv(modellLoc, 1, GL_FALSE, modelMat);








	  

Vertex Specification

Enable a generic vertex attribute array for vertex position

int posLoc = glGetAttribLocation(program, "vPos");
glEnableVertexAttribArray(posLoc);













	  

Vertex Specification

Specify location and data layout for a generic vertex array

int posLoc = glGetAttribLocation(program, "vPos");
glEnableVertexAttribArray(posLoc);
glBindBuffer(GL_ARRAY_BUFFER, posVBO);
glVertexAttribPointer(posLoc, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);











	  

Vertex Specification

Enable and specify data of a generic vertex attribute array for vertex color

int posLoc = glGetAttribLocation(program, "vPos");
glEnableVertexAttribArray(posLoc);
glBindBuffer(GL_ARRAY_BUFFER, posVBO);
glVertexAttribPointer(posLoc, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);

int colLoc = glGetAttribLocation(program, "vCol");
glEnableVertexAttribArray(colLoc);
glBindBuffer(GL_ARRAY_BUFFER, colVBO);
glVertexAttribPointer(posLoc, 4, GL_FLOAT, GL_FALSE, 0, (void*)0);






	  

Vertex Specification

Bind the IBO and render

int posLoc = glGetAttribLocation(program, "vPos");
glEnableVertexAttribArray(posLoc);
glBindBuffer(GL_ARRAY_BUFFER, posVBO);
glVertexAttribPointer(posLoc, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);

int colLoc = glGetAttribLocation(program, "vCol");
glEnableVertexAttribArray(colLoc);
glBindBuffer(GL_ARRAY_BUFFER, colVBO);
glVertexAttribPointer(posLoc, 4, GL_FLOAT, GL_FALSE, 0, (void*)0);

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vIndices);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, (void*)0);



	  

Vertex Specification

Release the vertex array attrbutes

int posLoc = glGetAttribLocation(program, "vPos");
glEnableVertexAttribArray(posLoc);
glBindBuffer(GL_ARRAY_BUFFER, posVBO);
glVertexAttribPointer(posLoc, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);

int colLoc = glGetAttribLocation(program, "vCol");
glEnableVertexAttribArray(colLoc);
glBindBuffer(GL_ARRAY_BUFFER, colVBO);
glVertexAttribPointer(posLoc, 4, GL_FLOAT, GL_FALSE, 0, (void*)0);

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vIndices);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, (void*)0);

glDisableVertexAttribArray(posLoc);
glDisableVertexAttribArray(colLoc);