Overview of a webgl program
by Lea Rosema
<canvas> element in your HTML and initialize a WebGL context from the JS side
Create a buffer containing vertex data for the kind of shape you want to display (eg two triangles forming a rectangle)
Bind buffers to vertex attributesanchor
Buffer data can be accessed by the vertex shader via attribute variables.
When a WebGL program is executed, the buffer is split into records (using a record size). These records are iterated through and passed to the vertex shader. The vertex shader is run multiple times, depending on how many records specified inside the buffer.
The record size depends on the data type of the attribute variable.
A number uses a record size of 1, a 2D vector (
vec2) has a record size of 2.
If you provide data for 3 coordinates making up a triangle, the vertex shader is executed 3 times and the attribute variable contains the coordinate of the nth record inside the buffer.
Set uniform variablesanchor
Set additional uniform variables, like the elapsed time. Another use case for uniform variables are for accessing texture data.
Setting the viewport sizeanchor
Initially and after resizing the WebGL canvas, you need to set the viewport size of the WebGL context.
Finally, you can draw all the things onto your canvas element via the
drawArrays in most cases.
These methods provide different draw modes:
POINTS: draw points on screen
LINES: draw lines on screen
TRIANGLES: draw filled triangles on screen
TRIANGLE_STRIP: like triangles, but the 4th record in the buffer reuses the 2nd and 3rd record in the buffer and so on.
drawArrays is called, the vertex and fragment shaders come into play.