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john_connor

OpenGL how to systematicaly draw objects with different programs/VAOs/set of uniforms

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hi,

i'm struggling with that question for a long time now. assume you have 2 programs (shader) and 2 vertex arrays to draw 2 different kind of things:

1. VAO: attributes are vec3 position, vec4 color

2. VAO: atributes are vec3 position, vec2 texturecoordinates, vec3 normals

both programs use different uniforms:

1. PROGRAM: mat4 transform

2. PROGRAM: mat4 transform, several material parameters, textures, lights, ...

drawcalls are the same for both ... how would you simplify that?

/// general draw call
struct DrawRangeElementsBaseVertex
{
	GLenum Mode = GL_POINTS;
	GLuint Start = 0;
	GLuint End = 0;
	GLsizei Count = 0;
	GLenum Type = GL_UNSIGNED_INT;
	const GLvoid* Indices = nullptr;
	GLint BaseVertex = 0;
};


/// general draw method
void Draw(const DrawElementsBaseVertex & cmd)
{
	glDrawElementsBaseVertex(cmd.Mode, cmd.Count, cmd.Type, cmd.Indices, cmd.BaseVertex);
}



/// (using PROGRAM 1 and VAO 1)
struct CDrawableNode
{
	/// world space transform
	glm::mat4 Transformation = glm::mat4(1);
	
	CMaterial Material;
	
	DrawRangeElementsBaseVertex MeshDrawCall;
};


/// (using PROGRAM 2 and VAO 2)
struct CDrawableGeometry
{
	/// world space transform
	glm::mat4 Transformation = glm::mat4(1);

	/// drawcall references
	std::vector<DrawRangeElementsBaseVertex> DrawCalls;
};

now i have 2 different for-loops for processing all the "CDrawableGeometry" and "CDrawableNode" in my scene. i'd like to do it with 1 big loop using "struct CRenderstates" somehow. has anybody some infos / links to useful sites / advices where to start with that ? somehow like:

for each renderstate ... set state

--> for each program/VAO ... use shader, bind program, set uniforms

----> for each object ... set program-specific uniforms, issue drawcalls

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Not sure what you're really asking, you pasted some source that doesn't really tell much - like what's your DrawableGeometry vs DrawableNode? What's the problem of doing it in one loop? Have you read about render queues, render items, sorting, state caching etc? 

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