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### #ActualYours3!f

Posted 04 January 2013 - 05:18 PM

GLuint vbo; //vertex buffer object containing the matrices
glGenBuffers( 1, &vbo ); //create the vbo

// I get the feeling that this line is the key. It is all important and it has the least amount of information available.
glBindBuffer(GL_ARRAY_BUFFER, vbo); //bind it

mat4 matrices[4];

/*
fill matrices here...
*/

//fill the vbo with data
glBufferData( GL_ARRAY_BUFFER, sizeof( float ) * 16 * 4, &matrices[0][0], GL_STATIC_DRAW );

//now that the matrices are on the GPU, lets go ahead and use them

//get the position of the vertex attribute to access the vbo
int pos1 = pos + 0; // <- According to mhagain, this gets the first row of the matrix specified in "transformmatrix".
int pos2 = pos + 1; // ... second row...
int pos3 = pos + 2; // ... third row...
int pos4 = pos + 3; // ... fourth row
glEnableVertexAttribArray(pos1);
glEnableVertexAttribArray(pos2);
glEnableVertexAttribArray(pos3);
glEnableVertexAttribArray(pos4);
// Now I am really confused. If I understand what mhagain wrote, each of these specify one row of a matrix.
// BUT...
// Each is setting the stride to be 16 floats! Is this a typo? What is happening here?

//set up the strides so that each vertex attribute location will point to each of the matrices.
//ie. pos1 --> matrices[0]
//pos2 --> matrices[1] etc...
glVertexAttribPointer(pos1, 4, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4 * 4, (void*)(0));
glVertexAttribPointer(pos2, 4, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4 * 4, (void*)(sizeof(float) * 4));
glVertexAttribPointer(pos3, 4, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4 * 4, (void*)(sizeof(float) * 8));
glVertexAttribPointer(pos4, 4, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4 * 4, (void*)(sizeof(float) * 12));

// This part I get...
glVertexAttribDivisor(pos1, 1);
glVertexAttribDivisor(pos2, 1);
glVertexAttribDivisor(pos3, 1);
glVertexAttribDivisor(pos4, 1);


I think this should work... haven't tested it though.

EDIT:
stride
Specifies the byte offset between consecutive generic vertex attributes. If stride is 0, the generic vertex attributes are understood to be tightly packed in the array. The initial value is 0.
this tells the api how big each data pack (each matrix) is

pointer
Specifies an offset of the first component of the first generic vertex attribute in the array in the data store of the buffer currently bound to the GL_ARRAY_BUFFER target. The initial value is 0.
ie this tells the api where each matrix is located in the vbo

### #2Yours3!f

Posted 04 January 2013 - 05:15 PM

GLuint vbo; //vertex buffer object containing the matricesglGenBuffers( 1, &vbo ); //create the vbo// I get the feeling that this line is the key. It is all important and it has the least amount of information available.glBindBuffer(GL_ARRAY_BUFFER, vbo); //bind itmat4 matrices[4];/*fill matrices here.....*///fill it with dataglBufferData( GL_ARRAY_BUFFER, sizeof( float ) * 16 * 4, &matrices[0][0], GL_STATIC_DRAW );//now that the matrices are on the GPU, lets go ahead and use them//get the position of the vertex attribute to access the vboint pos = glGetAttribLocation(shader_instancedarrays.program, "transformmatrix");int pos1 = pos + 0; // <- According to mhagain, this gets the first row of the matrix specified in "transformmatrix".int pos2 = pos + 1; // ... second row...int pos3 = pos + 2; // ... third row...int pos4 = pos + 3; // ... fourth rowglEnableVertexAttribArray(pos1);glEnableVertexAttribArray(pos2);glEnableVertexAttribArray(pos3);glEnableVertexAttribArray(pos4); // Now I am really confused. If I understand what mhagain wrote, each of these specify one row of a matrix.// BUT...// Each is setting the stride to be 16 floats! Is this a typo? What is happening here? //set up the strides so that each vertex attribute location will point to each of the matrices.//ie. pos1 --> matrices[0]//pos2 --> matrices[1] etc...glVertexAttribPointer(pos1, 4, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4 * 4, (void*)(0));glVertexAttribPointer(pos2, 4, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4 * 4, (void*)(sizeof(float) * 4));glVertexAttribPointer(pos3, 4, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4 * 4, (void*)(sizeof(float) * 8));glVertexAttribPointer(pos4, 4, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4 * 4, (void*)(sizeof(float) * 12)); // This part I get...glVertexAttribDivisor(pos1, 1);glVertexAttribDivisor(pos2, 1);glVertexAttribDivisor(pos3, 1);glVertexAttribDivisor(pos4, 1);
I think this should work... haven't tested it though.

EDIT:
stride
Specifies the byte offset between consecutive generic vertex attributes. If stride is 0, the generic vertex attributes are understood to be tightly packed in the array. The initial value is 0.
this tells the api how big each data pack (each matrix) is

pointer
Specifies an offset of the first component of the first generic vertex attribute in the array in the data store of the buffer currently bound to the GL_ARRAY_BUFFER target. The initial value is 0.
ie this tells the api where each matrix is located in the vbo

### #1Yours3!f

Posted 04 January 2013 - 05:07 PM

GLuint vbo; //vertex buffer object containing the matrices

glGenBuffers( 1, &vbo ); //create the vbo

// I get the feeling that this line is the key. It is all important and it has the least amount of information available.
glBindBuffer(GL_ARRAY_BUFFER, vbo); //bind it

mat4 matrices[4];

/*
fill matrices here.....
*/

//fill it with data
glBufferData( GL_ARRAY_BUFFER, sizeof( float ) * 16 * 4, &matrices[0][0], GL_STATIC_DRAW );

//now that the matrices are on the GPU, lets go ahead and use them

//get the position of the vertex attribute to access the vbo
int pos1 = pos + 0; // <- According to mhagain, this gets the first row of the matrix specified in "transformmatrix".
int pos2 = pos + 1; // ... second row...
int pos3 = pos + 2; // ... third row...
int pos4 = pos + 3; // ... fourth row
glEnableVertexAttribArray(pos1);
glEnableVertexAttribArray(pos2);
glEnableVertexAttribArray(pos3);
glEnableVertexAttribArray(pos4);

// Now I am really confused. If I understand what mhagain wrote, each of these specify one row of a matrix.
// BUT...
// Each is setting the stride to be 16 floats! Is this a typo? What is happening here?

//set up the strides so that each vertex attribute location will point to each of the matrices.
//ie. pos1 --> matrices[0]
//pos2 --> matrices[1] etc...
glVertexAttribPointer(pos1, 4, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4 * 4, (void*)(0));
glVertexAttribPointer(pos2, 4, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4 * 4, (void*)(sizeof(float) * 4));
glVertexAttribPointer(pos3, 4, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4 * 4, (void*)(sizeof(float) * 8));
glVertexAttribPointer(pos4, 4, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4 * 4, (void*)(sizeof(float) * 12));

// This part I get...
glVertexAttribDivisor(pos1, 1);
glVertexAttribDivisor(pos2, 1);
glVertexAttribDivisor(pos3, 1);
glVertexAttribDivisor(pos4, 1);

I think this should work... haven't tested it though.

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