Shaders

Shader objects in Dent represent complete shader programs: a vertex shader, possibly tesselation shaders and geometry shader, and a fragment shader. They are written in OpenGL Shader Language, with a small modification.

This guide assumes some knowledge of OpenGL shaders and pipelines. If you are new to all this, it is suggested to copy one of the shaders from an existing project and tweak it to your needs, or only use the builtin shaders.

Shader type	Filename	Required
Vertex	vertex.shd	Yes
Geometry	geometry.shd	No
Tesselation control	tesscontrol.shd	No
Tesselation evaluation	tesseval.shd	Only if control shader present
Fragment	fragment.shd	Yes

A simple vertex shader might look like this:

#version 400
in vec3 position;
out vec2 pos;

uniform mat3 model;

void main()
{
  gl_Position = vec4((model * position.xyz), 1);
  pos = position.xy/2+0.5;
}

The corresponding fragment shader might be:

#version 400
in vec2 pos;
out vec4 fragColor;

uniform sampler2D colormap;

void main()
{
  fragColor = texture(colormap, vec2(pos.x, 1-pos.y));
}

Note the output of the fragment shader is a vec4. You may output up to three vectors for defered rendering (see Render Pipelines).

Shaders are stored in the game tree under the folder shaders:

game
  ├── my-awesome-game.py
  ├── scenes
  │   ├── __init__.py
  │   └── MainScene.py
  └── shaders
      ├── image
      │   ├── fragment.shd
      │   └── vertex.shd
      └── ...

A shader object is created easily. For example to create a standard vertex-fragment shader and set some uniforms:

import dent.Shaders

...

shader = dent.Shaders.getShader('images')
shader['some_uniform'] = 1.4
shader['some_other_uniform'] = np.arange(1, 4, 0.3)

This corresponds to the shaders/image/* shader above.

The main function of shaders is the draw method. This loads the shader, sets the relevant uniforms and executes a glDraw* command. The precice command depends on the type of shader (generic, instanced, or feedback). Thus an object in the scene typically has a display function of the form:

def display(self):
  self.shader['model'] = self.model
  self.shader.draw(gl.GL_TRIANGLES, self.renderID)

For more detail, see the API documentation of the dent.Shaders package.