Program#

ModernGL is different from standard plotting libraries. You can define your own shader program to render stuff. This could complicate things, but also provides freedom on how you render your data.

Here is a sample program that passes the input vertex coordinates as is to screen coordinates.

Screen coordinates are in the [-1, 1], [-1, 1] range for x and y axes. The (-1, -1) point is the lower left corner of the screen.

Screen Coordinates

The screen coordinates#

The program will also process a color information.

Entire source

 1import moderngl
 2
 3ctx = moderngl.create_standalone_context()
 4
 5prog = ctx.program(
 6    vertex_shader='''
 7        #version 330
 8
 9        in vec2 in_vert;
10        in vec3 in_color;
11
12        out vec3 v_color;
13
14        void main() {
15            v_color = in_color;
16            gl_Position = vec4(in_vert, 0.0, 1.0);
17        }
18    ''',
19    fragment_shader='''
20        #version 330
21
22        in vec3 v_color;
23
24        out vec3 f_color;
25
26        void main() {
27            f_color = v_color;
28        }
29    ''',
30)

Vertex Shader

in vec2 in_vert;
in vec3 in_color;

out vec3 v_color;

void main() {
    v_color = in_color;
    gl_Position = vec4(in_vert, 0.0, 1.0);
}

Fragment Shader

in vec3 v_color;

out vec3 f_color;

void main() {
    f_color = v_color;
}

Proceed to the next step.