rvc.pt

01-07-2013, 07:33 AM

Hi,

I'm new to OpenGL and quaternions, but after doing some tutorials from opengl-tutorial, I'm trying to do the MVP with quats.

With the MVP I get the expected rotated triangle. But with quats I get a different rotation (I would link to an image, but seems I can't).

This is what I have in my C++ loop:

// Send our transformation to the currently bound shader,

// in the "MVP" uniform

glUniformMatrix4fv(MatrixID, 1, GL_FALSE, &MVP[0][0]);

// Let's try the same Matrix in Quat

glm::quat qModel = glm::gtx::quaternion::toQuat(MVP);

glm::gtc::quaternion::normalize(qModel);

glUniform4f(qModelID, qModel.x, qModel.y, qModel.z, qModel.w);

This is what I have in the shader:

// Values that stay constant for the whole mesh.

uniform mat4 MVP;

uniform vec4 qModel;

//rotate vector, taken from kri engine

vec3 qrot(vec4 q, vec3 v) {

return v + 2.0*cross(q.xyz, cross(q.xyz,v) + q.w*v);

}

void main(){

// Output position of the vertex, in clip space : MVP * position

//gl_Position = MVP * vec4(vertexPosition_modelspace, 1);

gl_Position = vec4(qrot(qModel, vertexPosition_modelspace),1);

}

Like you can see, for now, I just want to converted the MVP matrix to a Quat and use it in the shader, but I'm messing something up.

Any help would be appreciated.

Many thanks.

I'm new to OpenGL and quaternions, but after doing some tutorials from opengl-tutorial, I'm trying to do the MVP with quats.

With the MVP I get the expected rotated triangle. But with quats I get a different rotation (I would link to an image, but seems I can't).

This is what I have in my C++ loop:

// Send our transformation to the currently bound shader,

// in the "MVP" uniform

glUniformMatrix4fv(MatrixID, 1, GL_FALSE, &MVP[0][0]);

// Let's try the same Matrix in Quat

glm::quat qModel = glm::gtx::quaternion::toQuat(MVP);

glm::gtc::quaternion::normalize(qModel);

glUniform4f(qModelID, qModel.x, qModel.y, qModel.z, qModel.w);

This is what I have in the shader:

// Values that stay constant for the whole mesh.

uniform mat4 MVP;

uniform vec4 qModel;

//rotate vector, taken from kri engine

vec3 qrot(vec4 q, vec3 v) {

return v + 2.0*cross(q.xyz, cross(q.xyz,v) + q.w*v);

}

void main(){

// Output position of the vertex, in clip space : MVP * position

//gl_Position = MVP * vec4(vertexPosition_modelspace, 1);

gl_Position = vec4(qrot(qModel, vertexPosition_modelspace),1);

}

Like you can see, for now, I just want to converted the MVP matrix to a Quat and use it in the shader, but I'm messing something up.

Any help would be appreciated.

Many thanks.