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HermanssoN

std::vector and glUniformMatrix4fv

5 posts in this topic

Hello. I am trying to uppload an array of matrices to my glsl shader. I don't think my way of doing it is the correc way:

 

void Shader::setMatrixArray(std::string name, std::vector<glm::mat4>matrices)
{
	glUniformMatrix4fv(m_uniformLocation[name], matrices.size(), GL_FALSE,(float*)&matrices[0]);
	Helper::logError("failed to set matrix array");
}

if I check my list of uniform locations using a break point i noticed that, the g_skeleton (the matrix array) varible has the same location as my projection matrix:
 

+        [0]    ("g_projection", 0)    std::pair<std::basic_string<char,std::char_traits<char>,std::allocator<char> > const ,int>
+        [1]    ("g_skeleton", 0)    std::pair<std::basic_string<char,std::char_traits<char>,std::allocator<char> > const ,int>
+        [2]    ("g_view", 1)    std::pair<std::basic_string<char,std::char_traits<char>,std::allocator<char> > const ,int>
+        [3]    ("g_world", 2)    std::pair<std::basic_string<char,std::char_traits<char>,std::allocator<char> > const ,int>
 

 

Is this normal?

 

They are declared like this in my vertex shader:

#version 330

#define MAX_BONE_COUNT 40
uniform mat4     g_view;
uniform mat4     g_projection;
uniform mat4     g_world;
uniform mat4     g_skeleton[MAX_BONE_COUNT];

etc....

 

And just to be thorugh, this is how i save my uniforms:

bool Shader::addUniformVariable(std::string name)
{
	int location = glGetUniformLocation(m_program, name.c_str());
	Helper::logError("Shader::addUniformVariable() failed");
	
	if(location == -1)
	{
		return false;
	}
	m_uniformLocation[name] = location;
	return true;
}

If I dont use the matrix array evrything works just fine.

Edited by HermanssoN
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I found a solution:

Map the whole thing:

bool Shader::addMatrixArray(std::string name, int size)
{
	/* should not happen*/
	assert(name.size() < 128);

	std::map<std::string,int> locations;
	for(int i = 0; i<size; i++)
	{
		char n[128];
		sprintf_s(n, "%s[%d]", name.c_str(),i);
		int location = glGetUniformLocation(m_program,n);
		Helper::logError("Shader::addMatrixArray() failed");

		locations[n] = location;
	}
	m_uniformArrays[name] = locations; //map that contans a map indexed by name :)
	return true;
}

 

And setting the matrix array:

void Shader::setMatrixArray(std::string name, std::vector<glm::mat4>matrices)
{
	UniformMap map = m_uniformArrays[name];
        
        int size = matrices.size();
	int index = 0;
	UniformMap::iterator it = map.begin();
	while(it != map.end() && index != size)
	{
		int location = (*it).second;
		glUniformMatrix4fv(location, 1, GL_FALSE,glm::value_ptr(matrices[index]));
		Helper::logError("failed to set matrix array");
		
		index ++;
		it ++;
	}
}

If anyone knows a way to just uppload all tre matrices at once, pleas tell me smile.png
This seems to work for now.


 

Edited by HermanssoN
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If anyone knows a way to just uppload all tre matrices at once, pleas tell me smile.png

This seems to work for now.


 

 

glUniformMatrix4fv(location, 1, GL_FALSE,glm::value_ptr(matrices[index]));

 

The number in bold is the 'count' parameter - you can use it to upload several matrices at once.

 

If you need more fine-tuned control over your uniforms, look up uniform buffer objects (available from GL3.1).

Edited by irreversible
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Yes, as I did in my first post.
 

void Shader::setMatrixArray(std::string name, std::vector<glm::mat4>matrices)
{
	glUniformMatrix4fv(m_uniformLocation[name], matrices.size(), GL_FALSE,(float*)&matrices[0]);
	Helper::logError("failed to set matrix array");
}

My inital quastion was if this way of doing it was valid.

 

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Well, my problem might have been with glsl, not the glUniformMatrix4fv.

I filled my matrix array with the identity matrix and sent all 40 of them to the shader. Since all matrices where the same I only used one, e.g g_skeleton[0];

The shader will now optimize away unused variables, e.g
g_skeleton[1]->g_skeleton[MAX]. I did not realize this, I figured that if I used the g_skeleton variable all the uniforms world be "safe".

 

So when I sent my 40 matrices I overwrote my world, view and projection matrix. (this is my guess)

This code will not cause the shader to optimize away g_skeleton[1]->g_skeleton[MAX] since I use a variable as index.

position += (g_skeleton[index] * weight) * in_position

 

This code will:

position += (g_skeleton[0] * weight) * in_position

 

I used my original code:
 

void Shader::setMatrixArray(std::string name, std::vector<glm::mat4>matrices)
{
	glUniformMatrix4fv(m_uniformLocation[name], matrices.size(), GL_FALSE,(float*)&matrices[0]);
	Helper::logError("failed to set matrix array");
}

And I seems to work just fine.

Thank you for your help. Hope this post will help other to not do the same mistake.


I am not particularly fond of this optimizing away functionality, for debugging purposes one might want to be able to  simply comment out the usage of one particular variable, and then everything might stop working.

Edited by HermanssoN
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