Question

I’m currently trying to understand how to use the GLFrame Class in the superbible book, and acording to the 4th edition of the book, the camera matrix derived from the Frame of reference class should work the same as GluLookAt

When I add these lines

cameraFrame.SetForwardVector(-0.5f, 0.0f,-0.5f);
cameraFrame.Normalize();

The camera looks in the correct direction, yaw at 45 Degrees (Am I doing that right!)

However when I add this

cameraFrame.SetForwardVector(0.0f, 0.5f,-0.5f);

The camera just looks as if it was set to (0.0f, 0.0f, 1.0f)

Why is this! It’s been driving me mad for three days. Maybe I’m not passing in the vectors correctly, but I’m not sure how to pass in x,y 360 degrees for the look at (forward) location/vector. Do the vectors have to be normalized before passing them in?

Eventually I hope to do full mouse look (FPS style) , but for now just understanding why I can’t make the camera simply pitch up would be a good start.

Thansk!

Here is the code in situ.

// Called to draw scene
void RenderScene(void)
{
// Color values
static GLfloat vFloorColor[] = { 0.0f, 1.0f, 0.0f, 1.0f};
static GLfloat vTorusColor[] = { 1.0f, 0.0f, 0.0f, 1.0f };
static GLfloat vSphereColor[] = { 0.0f, 0.0f, 1.0f, 1.0f };

// Time Based animation
static CStopWatch   rotTimer;
float yRot = rotTimer.GetElapsedSeconds() * 60.0f;

// Clear the color and depth buffers
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);


// Save the current modelview matrix (the identity matrix)
modelViewMatrix.PushMatrix();   

M3DMatrix44f mCamera;

/////////
///////// My Code

cameraFrame.SetForwardVector(-0.5f,-0.5f,-0.5f);
cameraFrame.Normalize();

///////// End of my code
cameraFrame.GetCameraMatrix(mCamera);
modelViewMatrix.PushMatrix(mCamera);

// Transform the light position into eye coordinates
M3DVector4f vLightPos = { 0.0f, 10.0f, 5.0f, 1.0f };
M3DVector4f vLightEyePos;
m3dTransformVector4(vLightEyePos, vLightPos, mCamera);

// Draw the ground
shaderManager.UseStockShader(GLT_SHADER_FLAT,
                             transformPipeline.GetModelViewProjectionMatrix(),
                             vFloorColor);  
floorBatch.Draw();

for(int i = 0; i < NUM_SPHERES; i++) {
    modelViewMatrix.PushMatrix();
    modelViewMatrix.MultMatrix(spheres[i]);
    shaderManager.UseStockShader(GLT_SHADER_POINT_LIGHT_DIFF,     transformPipeline.GetModelViewMatrix(), 
                            transformPipeline.GetProjectionMatrix(), vLightEyePos, vSphereColor);
    sphereBatch.Draw();
    modelViewMatrix.PopMatrix();
    }

// Draw the spinning Torus
modelViewMatrix.Translate(0.0f, 0.0f, -2.5f);

// Save the Translation
modelViewMatrix.PushMatrix();

    // Apply a rotation and draw the torus
    modelViewMatrix.Rotate(yRot, 0.0f, 1.0f, 0.0f);
    shaderManager.UseStockShader(GLT_SHADER_POINT_LIGHT_DIFF, transformPipeline.GetModelViewMatrix(), 
                                 transformPipeline.GetProjectionMatrix(), vLightEyePos, vTorusColor);
    torusBatch.Draw();
modelViewMatrix.PopMatrix(); // "Erase" the Rotation from before

// Apply another rotation, followed by a translation, then draw the sphere
modelViewMatrix.Rotate(yRot * -2.0f, 0.0f, 1.0f, 0.0f);
modelViewMatrix.Translate(0.8f, 0.0f, 0.0f);
shaderManager.UseStockShader(GLT_SHADER_POINT_LIGHT_DIFF, transformPipeline.GetModelViewMatrix(), 
                            transformPipeline.GetProjectionMatrix(), vLightEyePos, vSphereColor);
sphereBatch.Draw();

// Restore the previous modleview matrix (the identity matrix)
modelViewMatrix.PopMatrix();
modelViewMatrix.PopMatrix();    
// Do the buffer Swap
glutSwapBuffers();

// Tell GLUT to do it again
glutPostRedisplay();

}

Answer 1

Thanks for everyones answers but the problem I had was this. In the openGL super bible, I was using their built in frame of reference class, and the problem I had was two functions, one called rotate, and rotateWorld.

I needed to use rotate for up/down movement, and rotateWorld for left right movement. This made the camera behave correctly (fly camera).

It makes sense as regardless of where you are looking up/down, you want the whole world to always spin around the vertical axis. Phew!