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The aim of my program is to render a simple colored triangle in rotation. The rotations are correct if all Z values of my vertices are equals to 0.0f. If one of these values are different of 0.0f the transformations are not correct (if I retreat the camera, the triangle seems to be in the same place).

The following declaration works correctly :

static GLfloat vertices[9] =
{
   -1.000000f, 0.000000f, 0.000000f,
    0.000000f, 1.000000f, 0.000000f,
    1.000000f, 0.000000f, 0.000000f
};

But the following one not works correctly :

static GLfloat vertices[9] =
{
    -1.000000f, 1.000000f, 1.000000f,
    -1.000000f, 1.000000f, -1.000000f,
    -1.000000f, -1.000000f, -1.000000f
};

So if the polygon is coplanar with the plane (x0y) it's ok, but in the other case it's not correct. I searched to find the problem in my matrix usage in vain. Here's a part of my code :

//Main loop

while (continuer)
{
    eventListener(&event, &continuer);

    glClearDepth(1.0f);
    glClearColor(0.13f, 0.12f, 0.13f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glUseProgram(programID);

    //Projection matrix

    glm::mat4 projection = glm::perspective(70.0f, ((float)WIDTH)/(float)HEIGHT, 1.0f, 1000.0f);

    //View matrix

    glm::mat4 view = glm::lookAt(glm::vec3(0.0f, 0.0f, trans), glm::vec3(0.0f, 0.0f, 0.0f), glm::vec3(0.0f, 1.0f, 0.0f));

    //Model matrix

    glm::mat4 model = glm::mat4(1.0f);
    model *= glm::translate(model, glm::vec3(0.0f, 0.0f, 0.0f));
    model *= glm::rotate(model, angle, glm::vec3(1.0f, 1.0f, 1.0f));

    glm::mat4 ModelViewMatrix = view * model;
    glm::mat4 ModelViewProjectionMatrix = projection * ModelViewMatrix;

    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, vertices);

    glEnableVertexAttribArray(1);
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 0, colors);

    glUniformMatrix4fv(glGetUniformLocation(programID, "MV"), 1, GL_TRUE, glm::value_ptr(ModelViewMatrix));
    glUniformMatrix4fv(glGetUniformLocation(programID, "MVP"), 1, GL_TRUE, glm::value_ptr(ModelViewProjectionMatrix));

    glDrawArrays(GL_TRIANGLES, 0, 3);

    glDisableVertexAttribArray(1);
    glDisableVertexAttribArray(0);

    glUseProgram(0);

    angle += 0.050000f;
    trans += 0.00010f;

    glFlush();
    SDL_GL_SwapBuffers();
}

and my vertex shader code :

#version 330

in vec3 VertexPosition;
in vec3 VertexColor;

uniform mat4 MV;
uniform mat4 MVP;

out vec3 Color;

void main()
{
    Color = VertexColor;

    gl_Position = MVP * vec4(VertexPosition, 1.0f);
}

I tried several combinations of code without any success. I'm lost. Does anyone can help me, please ?

Thanks very much in advance for your help.

share|improve this question
Can you explain how this is different from your other question? gamedev.stackexchange.com/questions/53341/… If it's not it should be removed and you should un-accept the other answer and update your question with whatever information it needs. – Byte56 Apr 5 at 20:20
I don't know anything about glm but why do you multiply at this point? model *= glm::rotate(model, angle, glm::vec3(1.0f, 1.0f, 1.0f)); Somehow I would expect this: model = glm::rotate(model, angle, glm::vec3(1.0f, 1.0f, 1.0f)); – Dirk Apr 5 at 20:27

1 Answer

up vote 1 down vote accepted

For me, this code looks flawed:

glm::mat4 model = glm::mat4(1.0f);
model *= glm::translate(model, glm::vec3(0.0f, 0.0f, 0.0f));
model *= glm::rotate(model, angle, glm::vec3(1.0f, 1.0f, 1.0f));

The modelviewmatrix you are creating seems to me to be like something as this:

M = I * T * (T * R)

(since glm::rotate(model, ...) creates the matrix T * R)

but I think you want to have something as this:

M = I * T * R

which would require the code ( = instead of *= ):

glm::mat4 model = glm::mat4(1.0f);
model = glm::translate(model, glm::vec3(0.0f, 0.0f, 0.0f));
model = glm::rotate(model, angle, glm::vec3(1.0f, 1.0f, 1.0f));
share|improve this answer
Thank you very much for your answer. I'm beginner in 3d space transformations. It works fine now. Good Bye. – user1450730 Apr 5 at 23:17

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