Is this the correct way to handle transformations in VBOs ?

Hello, im a new user, and currently im learning opengl.

Ive made a mesh in Blender and loaded it with a .obj parser that i made, i can now display the 3d model.
Then i wanted to make transformations. As you cant use inmediate mode with VBO i struggled until i came with a solution.

To handle rotations i made functions in my Mesh class, and i apply math directly to the vertex that i have loaded.

This is what my shaders looks like:

Vertex Shader:

#version 130

in vec4 vertexPosition;

void main()
	gl_Position.x = vertexPosition.x;
	gl_Position.y = vertexPosition.y;
	gl_Position.z = vertexPosition.z;
	gl_Position.w = 1.0;

Fragment Shader(only for color):

#version 130

out vec3 color;

void main()
	color = vec3(0.0,0.5,1.0);


This is how my functions look like:

(this is my calculateTranslation function)

void Modelo::calcularTraslado(float x, float y, float z)
glm::vec3 vectorTransf(x,y,z);

	for(unsigned int i=0; i<vertices.size(); i++)
     vertices[i] += vectorTransf;

	glBindBuffer(GL_ARRAY_BUFFER, _vboID);
	glBufferData(GL_ARRAY_BUFFER, vertices.size() * sizeof(glm::vec3), &vertices[0], GL_STATIC_DRAW); //GL buffer data takes position info?
	glBindBuffer(GL_ARRAY_BUFFER, 0);

Then the only thing i have to do is use my function (like this: calcularTraslado(1.0,1.0,1.0)) and i can translate the mesh in the space.

The problem is, i dont know if this is the correct way to do this, ive noticed that if i have a very large number of vertices to draw, the calculations take a lot of time, so i dont really know what can i do.

Thanks for take the time to read, and for the help!
Sorry for my bad english, im still learning it lol

The usual approach is to store the matrix in a uniform variable and have the vertex shader perform the transformation, e.g.

uniform mat4 transformation;
in vec4 vertexPosition;
void main()
	gl_Position = transformation * vertexPosition;

If you’re using the compatibility profile, you can still use the legacy OpenGL matrix functions (e.g. glTranslate()) and access the resulting matrices in the vertex shader, e.g either

	gl_Position = gl_ProjectionMatrix * gl_ModelViewMatrix * vertexPosition;


	gl_Position = gl_ModelViewProjectionMatrix * vertexPosition;

will transform the vertex position by the model-view and projection matrices, producing the same result as for legacy OpenGL.

[QUOTE=GClements;1272043]The usual approach is to store the matrix in a uniform variable and have the vertex shader perform the transformation, e.g.

uniform mat4 transformation;
in vec4 vertexPosition;
void main()
	gl_Position = transformation * vertexPosition;


And what does exactly the 4x4 matrix stores?, and how can i give values to it from the source?.

Thank you for the answer! :biggrin-new:

The transformation to be applied to the vertices.

With glUniformMatrix4fv().

[QUOTE=GClements;1272049]The transformation to be applied to the vertices.

With glUniformMatrix4fv().[/QUOTE]

Ive managed to make it run, but i cant see my mesh in the screen, i think i got something wrong, this is what i did:

I created a glm::mat4 transformation matrix(an identity matrix) in my Model class (private) and a function that returns that matrix ( ReturnMatrix():wink:

class Modelo

	void init(const char * ModelPath);

	void drawModel();

	//void calcularTraslado(float x, float y, float z);
	//void calcularEscala(float x, float y, float z);
	//void calcularRotacion(float x, float y, float z, float angle);
	glm::mat4 DevolverMatriz();

	std::vector< glm::vec3 > vertices;
	std::vector< glm::vec2 > uvs;
	std::vector< glm::vec3 > normals; // Won't be used at the moment.
	GLuint _vboID;
	glm::mat4 transformation;


Then i created a GLuint _MatrixID in my GLSLProgram and made a function “void recieveMatrix(glm::mat4 MyMatrix)”:

class GLSLProgram

	void compilarShaders(const std::string& VertexPath, const std::string& fragmentPath); //Funcion para compilar los txt cargados en opengl

	void linkearShaders(); //Linkear, combinar en un solo programa

	void agregarAtributo(const std::string& nombreAtributo); // Se bindean los atributos que hicimos en el shader a un index


	void recibirMatriz(glm::mat4 MiMatriz);


	int _numeroAtributos;
	void compilarShader(const std::string&  archivoPath, GLuint id); //Funcion para cargar los txt

	GLuint _shaderEnteroID;//EL PROGRAMA
	GLuint _vertexShaderID;// EL ID DEL SHADER VERTEX
	GLuint _fragmentShaderID; // EL ID DEL FRAGMENT SHADER
	GLuint _MatrixID;


void GLSLProgram::recibirMatriz(glm::mat4 MiMatriz)
	_MatrixID = glGetUniformLocation(_shaderEnteroID, "transformation");

then, in my main program, after linking the shaders i used recieveMatrix to give the vertexShader the values:

void JuegoPrincipal::initShaders()


But when i draw, i can only see the background, i think im doing something wrong, and the multiplication" transformation* vertexPosition"(in the shader) is sending the model to somewhere else. Maybe the “uniform mat4 transformation” its not recieving the values?

If the source code is needed just ask me and i will post it
Thank you

You need to call glUseProgram before you can make a glUniformMatrix call. Modern OpenGL also has glProgramUniform calls that don’t need the glUseProgram.

That did the trick!

Thank you guys so much!