Extend shaders support

[osrf-migration]

Original report (archived issue) by Ian Chen (Bitbucket: Ian Chen, GitHub: iche033).

---

from comment in pull request #55:

• While the ShaderParam currently encodes INT and FLOAT, it should probably be expanded to cover other commonly-used types with more than one value (Vector2, Vector3, Vector4, Matrix33, Matrix44)

• It may be useful to port the capabilities/features framework from ign-physics to the rendering system to indicate that some renderers don't support raw shaders (eg Optix):

  • ign-physics Feature (wip): https://github.com/ignitionrobotics/ign-physics/blob/e021b8d438af314c4862d757cb0719965578457b/include/ignition/physics/Feature.hh
  • Checking with OGRE: https://www.ogre3d.org/docs/api/1.9/class_ogre_1_1_render_system_capabilities.html

• Potentially expand for other shader types: Geometry, Compute, Tesselation

[osrf-migration]

Original comment by Nate Koenig (Bitbucket: Nathan Koenig).

---

• Edited issue description

[WilliamLewww]

Reference Branch

fragmentShaderParams Populating

I was digging around the uniform implementation and I noticed that the fragmentShaderParams (in OgreMaterial.cc) are created on demand.

void OgreMaterial::SetFragmentShader(const std::string &_path) in OgreMaterial.cc

  ...
  this->ogreMaterial->compile();
  this->ogreMaterial->load();

  this->fragmentShaderPath = _path;
  this->fragmentShaderParams.reset(new ShaderParams);
}

Since OGRE can query all the shader parameters, should we populate fragmentShaderParams after successfully compiling the shader?

Currently if you try to update a uniform that does not exist it will still be added to the fragmentShaderParams but OGRE will throw an error when trying to update the non-existent uniform.

Example Code:

  ir::ShaderParamsPtr shaderParams = shader->FragmentShaderParams();
  (*shaderParams)["thisUniformDoesNotExist"] = 0;

Output:
terminate call after throwing an instance of 'Ogre::InvalidParametersException' what(): OGRE EXCPETION(2:InvalidParametersException): Parameter called thisUniformDoesNotExist does not exist. in GpuProgramParameters::_findNamedConstantDefinition at /home/wlew/work/ogre-1.9/src/ogre-1.9.1/OgreMain/src/OgreGpuProgramParams.cpp (line 1725)

If we have a pre-existing list of all the uniforms, we could handle the error on ign-rendering rather than having OGRE handle it. Populating the fragmentShaderParams would also let us provide all the available uniforms for a shader program.

Support for 4-byte buffers

I have noticed that OGRE provides the following method which allows setting a uniform buffer of an arbitrary length:

void Ogre::GpuProgramParameters::setNamedConstant(const String& name, const int* val, size_t count, size_t multiple = 4)

I implemented an example on the reference branch that shows updating different uniform buffers with different sizes:

ign-rendering/examples/custom_shaders_uniforms/media/fragment_shader.glsl

uniform float testFloat;
uniform int testInt;
uniform float testFloatBuffer[6];
uniform int testIntBuffer[5];
uniform vec4 testVector4;
uniform mat4 textMatrix4;

void main()
{
  gl_FragColor = vec4(textMatrix4[0][0], textMatrix4[3][1], textMatrix4[3][3], 1.0);
}

ign-rendering/examples/custom_shaders_uniforms/GlutWindow.cc

  ir::ShaderParamsPtr shaderParams = shader->FragmentShaderParams();

  float testMatrix[16] = {
    0.1, 0.2, 0.3, 0.4,
    0.5, 0.6, 0.7, 0.8,
    0.9, 0.1, 0.2, 0.3,
    0.4, 0.5, 0.6, 0.7,
  };
  (*shaderParams)["textMatrix4"].InitializeBuffer(16);
  (*shaderParams)["textMatrix4"].UpdateBuffer(testMatrix, 16);

If we were to populate the fragmentShaderParams after compiling the shader program, the InitializeBuffer method call could be removed from the user application because OGRE can query the size of a buffer.

[chapulina]

If we have a pre-existing list of all the uniforms, we could handle the error on ign-rendering rather than having OGRE handle it.

+1. And I think it may also be a good idea to have a safety catch in case something shows up that we don't know about, so we don't just crash on the user.

Reference Branch

How about opening a pull request so we can iterate on it?