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## need help with rotation, transformation and scaling in opengl mathematics

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### #1MrDarkKnight  Members

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Posted 25 January 2012 - 03:30 AM

Hello guys

OpenGL 4.2 is basically killing me, I can't rotation, transformation or scaling, I have to use another library to do it, which is OpenGL mathematics. And I can't find any tutorials on how to do this.

I miss OpenGL 2.1.

Can you please guys help me out here.

I have this cube and I want to rotate it how can I do that in OpenGL mathematics?

void Engine::CreateCube()
{
float* Vertices = new float[72];  // Vertices for our square

Vertices[0]  = -0.3f; Vertices[1]  = -0.3f; Vertices[2]  = 0.3f;
Vertices[3]  =  0.3f; Vertices[4]  = -0.3f; Vertices[5]  = 0.3f;
Vertices[6]  =  0.3f; Vertices[7]  =  0.3f; Vertices[8]  = 0.3f;
Vertices[9]  = -0.3f; Vertices[10] =  0.3f; Vertices[11] = 0.3f;

Vertices[12] = -0.3f; Vertices[13] = -0.3f; Vertices[14] = -0.3f;
Vertices[15] = -0.3f; Vertices[16] =  0.3f; Vertices[17] = -0.3f;
Vertices[18] =  0.3f; Vertices[19] =  0.3f; Vertices[20] = -0.3f;
Vertices[21] =  0.3f; Vertices[22] = -0.3f; Vertices[23] = -0.3f;

Vertices[24] = -0.3f; Vertices[25] = 0.3f;  Vertices[26] = -0.3f;
Vertices[27] = -0.3f; Vertices[28] = 0.3f;  Vertices[29] =  0.3f;
Vertices[30] =  0.3f; Vertices[31] = 0.3f;  Vertices[32] =  0.3f;
Vertices[33] =  0.3f; Vertices[34] = 0.3f;  Vertices[35] = -0.3f;

Vertices[36] = -0.3f; Vertices[37] = -0.3f; Vertices[38] = -0.3f;
Vertices[39] =  0.3f; Vertices[40] = -0.3f; Vertices[41] = -0.3f;
Vertices[42] =  0.3f; Vertices[43] = -0.3f; Vertices[44] =  0.3f;
Vertices[45] = -0.3f; Vertices[46] = -0.3f; Vertices[47] =  0.3f;

Vertices[48] = 0.3f;  Vertices[49] = -0.3f; Vertices[50] = -0.3f;
Vertices[51] = 0.3f;  Vertices[52] =  0.3f; Vertices[53] = -0.3f;
Vertices[54] = 0.3f;  Vertices[55] =  0.3f; Vertices[56] =  0.3f;
Vertices[57] = 0.3f;  Vertices[58] = -0.3f; Vertices[59] =  0.3f;

Vertices[60] = -0.3f; Vertices[61] = -0.3f; Vertices[62] = -0.3f;
Vertices[63] = -0.3f; Vertices[64] = -0.3f; Vertices[65] =  0.3f;
Vertices[66] = -0.3f; Vertices[67] =  0.3f; Vertices[68] =  0.3f;
Vertices[69] = -0.3f; Vertices[70] =  0.3f; Vertices[71] = -0.3f;

glGenVertexArrays(1, &VAO_ID[0]); // Create our Vertex Array Object
glBindVertexArray(VAO_ID[0]); // Bind our Vertex Array Object so we can use it

glGenBuffers(1, VBO_ID); // Generate our Vertex Buffer Object
glBindBuffer(GL_ARRAY_BUFFER, VBO_ID[0]); // Bind our Vertex Buffer Object
glBufferData(GL_ARRAY_BUFFER, 72 * sizeof(GLfloat), Vertices, GL_STATIC_DRAW); // Set the size and data of our VBO and set it to STATIC_DRAW

glVertexAttribPointer((GLuint)0, 3, GL_FLOAT, GL_FALSE, 0, 0); // Set up our vertex attributes pointer
glEnableVertexAttribArray(0); // Disable our Vertex Array Object
glBindVertexArray(0); // Disable our Vertex Buffer Object

delete [] Vertices; // Delete our vertices from memory
}


In my redner function which draws the cube i tried doing this but nothing changes.
void Engine::Render()
{
glViewport(0, 0, WindowWidth, WindowHeight);

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

ViewMatrix = glm::translate(glm::mat4(1.0f), glm::vec3(0.0f, 0.0f, -5.f)); // Create our view matrix which will translate us back 5 units
ModelMatrix = glm::scale(glm::mat4(1.0f), glm::vec3(0.5f));  // Create our model matrix which will halve the size of our model

glm::mat4 View = glm::mat4(1.);
View = glm::rotate(View, angle * -1.0f, glm::vec3(1.f, 0.f, 0.f));

glBindVertexArray(VAO_ID[0]); // Bind our Vertex Array Object

glDrawArrays(GL_QUADS, 0, 24); // Draw our cube

glBindVertexArray(0); // Unbind our Vertex Array Object

}


### #2guptan  Members

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Posted 25 January 2012 - 07:21 AM

You must be knowing how to write shaders for opengl 4.2 and make it running.
Try a port of the following code(most probably no change), for matrix calculations (translation, rotation, scaling etc.) to get

### #3MrDarkKnight  Members

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Posted 25 January 2012 - 08:12 AM

You must be knowing how to write shaders for opengl 4.2 and make it running.
Try a port of the following code(most probably no change), for matrix calculations (translation, rotation, scaling etc.) to get
http://opengles-book...n/esTransform.c

so if i don't use shaders i can't do translation, rotation or scaling?
what is sharder? what is the use of them?

sorry for the newbie questions.

### #4Yours3!f  Members

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Posted 25 January 2012 - 09:02 AM

so if i don't use shaders i can't do translation, rotation or scaling?
what is sharder? what is the use of them?

sorry for the newbie questions.

ummm... shaders aren't responsible for translation rotation etc. but rendering. Math libraries are supposed to handle this stuff. You can find many math libraries that replace the built-in opengl maths.
To mention a few: GLM, CML, Eigen, libmymath
A shader is a tiny program that runs on your video card. It supposed to replace the fixed pipeline rendering that you used in OGL 2.1.
It has many advantages over the old rendering one being the great flexibility it offers when it comes to rendering.

### #5V-man  Members

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Posted 25 January 2012 - 11:02 AM

Sig: http://glhlib.sourceforge.net
an open source GLU replacement library. Much more modern than GLU.
float matrix[16], inverse_matrix[16];
glhTranslatef2(matrix, 0.0, 0.0, 5.0);
glhScalef2(matrix, 1.0, 1.0, -1.0);
glhQuickInvertMatrixf2(matrix, inverse_matrix);
glUniformMatrix4fv(uniformLocation1, 1, FALSE, matrix);
glUniformMatrix4fv(uniformLocation2, 1, FALSE, inverse_matrix);

### #6MrDarkKnight  Members

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Posted 25 January 2012 - 11:10 AM

thank you guptan but i would like to know how to rotate the cube using OpenGL Mathematics (GLM) library.

can anyone tell me how can rotate my cube using OpenGL Mathematics (GLM) library?

### #7japro  Members

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Posted 25 January 2012 - 11:35 AM

OpenGL 4.2 pretty much deprecates the fixed pipeline so you have to write shaders. The way you do transforms then is by passing the transformation matrix to the shader which then applies it to the vertices during rendering.

### #8MrDarkKnight  Members

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Posted 25 January 2012 - 11:37 AM

OpenGL 4.2 pretty much deprecates the fixed pipeline so you have to write shaders. The way you do transforms then is by passing the transformation matrix to the shader which then applies it to the vertices during rendering.

oo ok thank you very much.

thank you guys for all your help.

### #9clb  Members

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Posted 25 January 2012 - 11:47 AM

To mention a few: GLM, CML, Eigen, libmymath

If you are allergic to templates or are looking for an online reference of copy-paste code, you can also have a look at MathGeoLib.
Me+PC=clb.demon.fi | C++ Math and Geometry library: MathGeoLib, test it live! | C++ Game Networking: kNet | 2D Bin Packing: RectangleBinPack | Use gcc/clang/emcc from VS: vs-tool | Resume+Portfolio | gfxapi, test it live!

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