OpenGL GLSL using projection,view and transformation

Question

I have been trying to get a simple triangle to render on the screen. I am using Projection, View and Transformation matrices but am unable to get anything to the screen.

Main loop

...
shader->start();

Matrix4f transformation = Math::createTransformationMatrix(Vec3<float>(0,0,-25),0,0,0, 1);
shader->loadTransformationMatrix(transformation);

Matrix4f camera = Math::createViewMatrix(Vec3<float>(0, 0, 0), 1, 0, 0);
shader->loadViewMatrix(camera);

Matrix4f projection = Math::getProjectionMatrix(1080,720);
shader->loadProjectionMatrix(projection);

glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glVertexAttribPointer(
    0, 
    3,
    GL_FLOAT,
    GL_FALSE,
    0,
    (void*)0
);
glDrawArrays(GL_TRIANGLES, 0, 3);
glDisableVertexAttribArray(0);

shader->stop();
...

Math.h

static Matrix4f createTransformationMatrix(Vec3<float> translation, float rx, float ry, float rz, float scale) {
    Matrix4f matrix;
    Matrix4f::translate(translation, matrix,matrix);
    Matrix4f::rotate(toRadians(rx), Vec3<float>(1, 0, 0), matrix, matrix);
    Matrix4f::rotate(toRadians(ry), Vec3<float>(0, 1, 0), matrix, matrix);
    Matrix4f::rotate(toRadians(rz), Vec3<float>(0, 0, 1), matrix, matrix);
    Matrix4f::scale(Vec3<float>(scale, scale, scale), matrix, matrix);
    return matrix;
}
static Matrix4f createViewMatrix(Vec3<float> pos, float pitch, float yaw, float roll) {
    Matrix4f matrix;
    Matrix4f::rotate(toRadians(pitch), Vec3<float>(1, 0, 0), matrix, matrix);
    Matrix4f::rotate(toRadians(yaw), Vec3<float>(0, 1, 0), matrix, matrix);
    Matrix4f::rotate(toRadians(roll), Vec3<float>(0, 0, 1), matrix, matrix);

    Vec3<float> negativeCam(-pos.x, -pos.y, -pos.z);
    Matrix4f::translate(negativeCam, matrix, matrix);

    return matrix;
}
static Matrix4f getProjectionMatrix(int width, int height) {
    float aspectRatio = (float)width / (float)height;
    float y_scale = (float)((1 / tan(toRadians(FOV / 2)))*aspectRatio);
    float x_scale = y_scale / aspectRatio;
    float frustum_length = FAR_PLANE - NEAR_PLANE;

    Matrix4f projectionMatrix;
    projectionMatrix[0] = x_scale;
    projectionMatrix[5] = y_scale;
    projectionMatrix[10] = -((FAR_PLANE + NEAR_PLANE) / frustum_length);
    projectionMatrix[11] = -1;
    projectionMatrix[14] = -((2 * NEAR_PLANE * FAR_PLANE) / frustum_length);
    projectionMatrix[15] = 0;
    return projectionMatrix;
}

Vertex Shader

    #version 330 core

    layout(location = 0) in vec3 position;

    uniform mat4 transformationMatrix;
    uniform mat4 projectionMatrix;
    uniform mat4 viewMatrix;

    void main() {
        //Works but renders without any camera or projection applied
        //gl_Position.xyz = position;
        //gl_Position.w = 1.0;

        vec4 worldPosition = transformationMatrix * vec4(position, 1.0);
        vec4 positionRelitiveToCam = viewMatrix * worldPosition;
        gl_Position = projectionMatrix * positionRelitiveToCam;
    }

Answer 1

Some sanity checks could help you debug this:

1. Disable culling with glDisable( GL_CULL_FACE );
2. Disable depth test with glDisable( GL_DEPTH_TEST );
3. Use super simple fragment shader that just sets frag colour to (1.0, 0.0, 0.0, 1.0) e.g.

If after that, you still only see a black screen, double check your view matrix.

Something that not everybody may know: the view matrix is nothing else than the inverse of your camera transform.

So instead of building up your viewmat as in your code, it is easier to just transform (position/orient) your camera in the world. Then take its matrix, and invert it.

That inverted matrix, is your view matrix.

Answer 2

There are many things that can be wrong, check the follows:

• Use quaternions, because then you can normalize them and be sure that all is correct.
• gl_position should look like this: ViewProjection * cameraRotation * cameraTranslation * Object transformation * vec4(Position,1.0);

Where object transformation is: Object Translation * Object Rotation * Object Scale

• Stop using glUseProgram(0) Opengl is sequential, it wont do anything good for you.

• Make a buffer at the init to initializate the vertex buffer and save it for later use it. It should look something like this:

  glGenVertexArrays(1, &m_VAO); glBindVertexArray(m_VAO); glBindBuffer(GL_ARRAY_BUFFER, m_Buffers[POS_VB]); glBufferData(GL_ARRAY_BUFFER, sizeof(Positions[0]) * Positions.size(), &Positions[0], GL_STATIC_DRAW); glEnableVertexAttribArray(POSITION_LOCATION); glVertexAttribPointer(POSITION_LOCATION, 3, GL_FLOAT, GL_FALSE, 0, 0);