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Answer some NOOB question xD


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#1 João Martins   Members   -  Reputation: 100

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Posted 31 March 2012 - 07:45 PM

Hi all,

I'm relatively new to OpenGL and GLSL, and I have some work to be delivered by Monday, and I'm having a trouble that I can't figure out, and hope you guys could help.

So I have two meshes, a spaceship and a sun, loaded, two different VAO (I know, lame, but for now I can't do different), and in my display func, I'm doing some matrix transformations to these 2 meshes, different to booth. They're good for each of the meshs but when I put the two together, the spaceship got's translated somewhere near the sun, and it is supposed to be at the origin. I know this is probably by my vertex shader, I will paste the code:

layout (location=0) in vec4 vertex;
layout (location=1) in vec3 color;
layout (location=2) in vec4 vertex2;
layout (location=2) in vec3 color2;
out vec4 color_vf;
out vec4 color_vf2;
uniform mat4 pMatrix;
uniform mat4 vMatrix;
uniform mat4 mMatrixSpaceship;
uniform mat4 mMatrixSun;
void main()
{
color_vf = vec4(color,1.0f);
color_vf2 = vec4(0.5f , 0.5f ,0.0f ,1.0f);

gl_Position =(pMatrix * vMatrix * mMatrixSun * vertex2) + (pMatrix * vMatrix * mMatrixSpaceship * vertex)  ;
 

}

The vertex is the spaceship, vertex2 the sun. pMatrix perspective, and vMatrix view, the rest I think is fairly obvious.
I've tried to render the two separately, but I can't find any USEFUL documentation in the net (at least the way I'm learning, wich is kind onorthodox :/)

So I would appreciate if any of you guys didn't mind helping a bit, I would be very thankful, and I think this is a good comunity to be, maybe one day I'll answer some of my one :)

Thankz
Juca

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#2 João Martins   Members   -  Reputation: 100

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Posted 01 April 2012 - 07:36 AM

Does not anyone have an idea on how to solve this? Not a single feedback?

I would really apreeciate.

#3 flodihn   Members   -  Reputation: 243

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Posted 01 April 2012 - 08:41 AM

Hmm, what you usually do in openGL is something like this, this is a bit pseudo code:

void displayCallback() {
    glTranslatef(sun_posx, sun_posy, sun_posz); // Move to the coordinates where you want to draw the sun 
    drawSun();

    glLoadIdentity(); // This resets opengl's position to 0, 0,0 again

    glTranslate3f(space_ship_posx, space_ship_posy, space_ship_posz) // Move where you want to draw the ship
    drawShip();
}

I think with your function:
gl_Position =(pMatrix * vMatrix * mMatrixSun * vertex2) + (pMatrix * vMatrix * mMatrixSpaceship * vertex)  ;
You tell openGL to move the the suns position AND ships position and draw everything there.

#4 João Martins   Members   -  Reputation: 100

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Posted 01 April 2012 - 10:25 AM

That works with stock shaders, not with my vertex shader. The way you're doing (if i'm correct), for each mesh, when you do the draw, you use the same shader, but different instances (your obj class have a draw function, mine doesn´t, I use glDrawElements with the attributes in the sahder). I understand that the transformation WOULD be applied to both (is that why we use stack for the matrix transformation), but the ship should be transported to the exact same position as the sun, but it is transformed somewhat like a vector with the same direction, but like 75% of the distance.

I'll put the OpenGL code:

glUseProgram(programId);
GLuint loc = glGetUniformLocation(programId, "pMatrix");
glUniformMatrix4fv(loc, 1, GL_FALSE, (GLfloat *)&perspectiveMatrix[0]);
loc = glGetUniformLocation(programId, "vMatrix");
glUniformMatrix4fv(loc, 1, GL_FALSE, (GLfloat *)&cameraMatrix[0]);
/*
  !![NEW]!!
  Get the location of the model matrix in the shader
*/
 
loc = glGetUniformLocation(programId, "mMatrixShip");
/*
  end !![NEW]!!
*/
glBindVertexArray(vaoObject1);
//Spaceship Movement
//These rotation are meant to orientate the spaceship to it's original spot.
glm::mat4 rotateZ = glm::rotate(glm::mat4(1.0), 180.0f, glm::vec3(0.0f, 0.0f, 1.0f));
glm::mat4 rotateX = glm::rotate(glm::mat4(1.0), 90.0f, glm::vec3(1.0f, 0.0f, 0.0f));
//These are the move transformations. As the keys are being pressed, the Move Struct is being altered, and these matrix are constructed with those arguments
glm::mat4 rotateShip = glm::rotate(glm::mat4(1.0), ship.angle, glm::vec3(0.0f, 0.0f, -1.0f));
glm::mat4 moveShip = glm::translate(glm::mat4(1.0), glm::vec3(ship.X,ship.Y,0.0));


//Applying the rotation to the spaceship, so it's oriented as wanted, then apply the movement transformation.

glm::mat4 model = moveShip * rotateShip * rotateZ * rotateX ;
//Pass the modelTransformations(shipMovemnt) matrix to the shader

glUniformMatrix4fv(loc, 1, GL_FALSE, (GLfloat *)&model[0]);
glDrawElements(GL_TRIANGLES, spaceShip.IndexArray.size(), GL_UNSIGNED_INT, &(spaceShip.IndexArray[0])); //type of geometry; number of indices; type of indices array, indices pointer

glBindVertexArray(0);
//Sun Drawing and Transformations
glBindVertexArray(vaoObject2);
loc = glGetUniformLocation(programId, "mMatrixSun");
/*Matrix for sun Transformations, 'hand-crafted'
GLfloat sunScale[] = { 5.0f, 0.0f, 0.0f, 0.0f,
		 0.0f, 5.0f, 0.0f, 0.0f,
		 0.0f, 0.0f, 5.0f, 0.0f,
		 0.0f, 0.0f, 0.0f, 1.0f};
GLfloat sunTranslation[] = { 1.0f, 0.0f, 0.0f, 15.0f,
	    0.0f, 1.0f, 0.0f, -15.0f,
	    0.0f, 0.0f, 1.0f, 0.0f,
	    0.0f, 0.0f, 0.0f, 1.0f};
*/

glm::mat4 sunTranslation = glm::translate(glm::mat4(1.0), glm::vec3(-15,15.0,0.0));
glm::mat4 sunScale = glm::scale(glm::mat4(1.0), glm::vec3(5,5,5));
glm::mat4 sunModel = sunTranslation * sunScale;


glUniformMatrix4fv(loc, 1, GL_FALSE, (GLfloat *)&sunModel[0]);

glDrawElements(GL_TRIANGLES, sun.IndexArray.size(), GL_UNSIGNED_INT, &(sun.IndexArray[0]));
glBindVertexArray(0);

The commented Matrix for display, our teacher obligates (as she should) to know all the linear algebra parts of graphics.
Thankz for the tips anyway, I'll try the Loadentity, I wasn´t reseting the origin.

#5 João Martins   Members   -  Reputation: 100

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Posted 01 April 2012 - 10:49 AM

I've solved the problem other way. I loaded again the program (Vetex Shader+Frag Shader) for each object, and passed the transformations. That way the program is always fresh and clean for each vertex ; )

Meanwhile, you could give some other solutions, are always aprecciated ;)

Thankz for the tips, even brief ones.




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