Shaders and Materials

In rendering pipelines, the shader is responsible for determining how the brightness and color of objects changes when light is cast on them.

Important

Currently shaders are only implemented for 3-D objects! 2-D objects do not interact with lighting.

By default, Algan will use the default_shader() function to shade Mobs. This function implements a simplified diffusion shader, which does not depend on any material properties. This means that all objects will interact with light in the same way.

If you want to get more realistic lighting, you can use more sophisticated shaders that take into consideration the material properties of the object.

Using a Physics-based Rendering Shader

Algan also provides a basic implementation of a physics-based shader in the basic_pbr_shader() function. This function takes an additional 2 parameters as input compared to the default shader: metallicness and smoothness. This function simulates how light interacts with a surface made of metal vs non-metal and smooth vs rough texture to compute diffuse and specular lighting effects.

You can make a mob use this shader with the set_shader() method. Let’s look at an example.

Example: SetShader

from algan import *
from algan.rendering.shaders.pbr_shaders import basic_pbr_shader

with Sync():
    mob1 = Sphere().move(LEFT*2).spawn()
    mob2 = Sphere().move(RIGHT*2).set_shader(basic_pbr_shader).spawn()

with Seq(run_time_unit=5):
    mob2.smoothness = 0
    mob2.metallicness = 1
    mob2.smoothness = 1
    mob2.metallicness = 0

render_to_file()

from algan import *
from algan.rendering.shaders.pbr_shaders import basic_pbr_shader

with Sync():
    mob1 = Sphere().move(LEFT*2).spawn()
    mob2 = Sphere().move(RIGHT*2).set_shader(basic_pbr_shader).spawn()

with Seq(run_time_unit=5):
    mob2.smoothness = 0
    mob2.metallicness = 1
    mob2.smoothness = 1
    mob2.metallicness = 0

render_to_file()

Important

You must use set_shader() before spawning the mob! Once spawned, the shader cannot be changed.

In this example, the first mob (left) uses the default shader, and the second (right) uses the PBR shader, with a range of different material properties. Note that the smoothness and metallicness attributes are not methods of the Mob class. When we called the set_shader() method, it read the the function signature of the shader and realised that there were 2 additional arguments named smoothness and metallicness, so it automatically added those as animatable attributes to our mob.

Writing Custom Shaders

If you want to make your own shader, all you need to do is implement the function for it. Take a look at the source code for default_shader() and basic_pbr_shader() functions to see how this can be done in Pytorch. If you make your own shader function, it must have the same signature as the default shader, plus any additional shader parameters you require. Even if you don’t use them, your function signature must still declare the default parameters. Any new parameters you introduce beyond those in the default_shader() will be automatically added as animatable attributes to your mobs when you set this function as their shader.

Once you’ve defined your shader function, simply use set_shader() as in the above example. You can then animate any shader parameters just as you would any of the built in animatable attributes.

Note

During rendering, mobs with different shaders will be batched separately. This means you should reuse the same function definition where possible, as it will allow mobs to be batched more effectively.