Single shader per model in OpenGL

Question

First of all, I have a camera object with a method called GetViewProj() to get the projection*view matrix.

I have also created a shaderprogram object to handle compilation and linking of a shader and setting uniforms and attributes. Each model has an instance of this shaderprogram to handle a specific shader.

I would like to be able to be able to render the scene like the following:

void RenderScene(){

  ModelA->Render();
  ModelB->Render();
}

What I want to know is how to properly tie in the view and projection to these models.Do I just do the following for each model in the RenderScene function:

ModelA->shaderprogram->setUniform("viewProj",Camera->GetViewProj());
ModelB->shaderprogram->setUniform("viewProj",Camera->GetViewProj());

I would also like to know if there is a better method in general when comes to setting this up.

Answer 1

My interpretation of a given model's Render function would be that it should be responsible for all the actions required for performing the render, so rather than setting your view projections at the beginning of your render scene call (which, btw means all of your models have to be defined in world space, which is unsavory), I would have it the responsibility of the Render function to go out and get the current modelview matrix.

In my applications I have a Stacks singleton type which has a static access method to fetch the instance. I don't bind my shaders to the models themselves, so I use a render helper method that accepts both a mesh and a Shader program.

void GlUtils::renderGeometry(
  const GeometryPtr & geometry,
  ShaderResource vs, 
  ShaderResource fs) 
{
  ProgramPtr program = GlUtils::getProgram(vs, fs);
  program->use();
  // apply lighting model uniforms
  Stacks::lights().apply(program);
  // apply the current projection matrix
  Stacks::projection().apply(program);
  // apply the modelview matrix
  Stacks::modelview().apply(program);
  // This compares the list of uniforms in the program with what I've bound.  
  // If I haven't configured some it will warn me.
  program->checkConfigured();

  // draw the actual model
  geometry->bindVertexArray();
  geometry->draw();

  // restore the OpenGL state 
  VertexArray::unbind();
  Program::clear();
}

Your model Render method could similarly reach out to a singleton and fetch the appropriate matrix, so that you're not responsible for managing it at the renderScene level.