2. First Triangle

Add GLEW

The OpenGL Extension Wrangler Library (GLEW) is a cross-platform open-source C/C++ extension loading library. GLEW provides efficient run-time mechanisms for determining which OpenGL extensions are supported on the target platform.

Download the library from the above link and add it to your project.

Note: If you use the static library of GLEW - glew32s.lib, you have to set the GLEW_STATIC in the preprocessor. Otherwise it won’t work

Point

Now all is set, let’s draw one single point in the window to get a sense of how OpenGL works.

Include your library

#include <GL/glew.h>

Initialize GLEW

if (glewInit() != GLEW_OK)
{
  return 1;
}

Create the point

Consider the point is 3-dimensional point at (0.0, 0.0, 0.0).

static const GLfloat vertices[] = {
    0.0f, 0.0f, 0.0f,
}

Generate a Vertex Buffer Object

Vertex Buffer Object is the way you send your data to GPU. We store our vertices data in the buffer and submit the buffer to GPU.

GLuint VBO;
glGenBuffers(1, &VBO)
// the first parameter is the how many Vertex Buffer Objects you want to generate. The second parameter is the buffer.

Bind buffer

The buffer is generated in a generic way. It doesn’t know what type of the data is. It’s the job of the next function to tell the buffer what we intend to do with the buffer.

glBindBuffer(GL_ARRAY_BUFFER, VBO);

// Tell GPU the data to store in it is an array of vertices.

Bind data

Now we are going to bind our data to the buffer.

glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

Enable Vertex Attributes

Following code is to write in the main loop.

By default of the pipeline, for vertices without shader the index we are referring to is 0.

glEnableVertexAttribArray(0);

Interpretation of the data

Tell GPU how to interpret the data in buffer.

glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);

The first parameter: index of the attribute The second parameter: number of components(3 for X, Y and Z) The third parameter: data type of each component The forth parameter: weather to be normalized before it is used in the pipeline. The fifth parameter: stride The sixth parameter: array buffer offset.

Draw the Point

glDrawArrays(GL_POINTS, 0, 1);

Now you should see a point in the middle of the window.

Draw the triangle

replace the data point with

static const GLfloat vertices[] = {
    0.0f, 1.0f, 0.0f,
    -1.0f, 0.0f, 0.0f,
    1.0f, 0.0f, 0.0f,
};

And the draw function.

glDrawArrays(GL_TRIANGLES, 0, 3);

Then you should see