I have this function which draws a small 3D axis coordinate system on the bottom left corner of the screen but depending on what I have in front of me, it may get clipped.
For instance, I have drawn a plain terrain on the ground, on the XZ plane at Y = 0. The camera is positioned on Y = 1.75 (to simulate an average person's height). If I'm looking up, it works fine, if I'm looking down, it gets clipped by the ground plane.
Looking up: https://i.sstatic.net/Q0i6g.png
Looking down: https://i.sstatic.net/D5LIx.png
The function I call to draw the axis system on the corner is this:
void Axis3D::DrawCameraAxisSystem(float radius, float height, const Vector3D rotation) {
if(vpHeight == 0) vpHeight = 1;
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glViewport(0, 0, vpWidth, vpHeight);
gluPerspective(45.0f, 1.0 * vpWidth / vpHeight, 1.0f, 5.0f);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0f, 0.0f, -3.0f);
glRotatef(-rotation.x, 1.0f, 0.0f, 0.0f);
glRotatef(-rotation.y, 0.0f, 1.0f, 0.0f);
DrawAxisSystem(radius, height);
}
An now a couple of main functions I think are relevant to the problem:
glutDisplayFunc(renderScene);
glutReshapeFunc(changeSize);
void changeSize(int width, int height) {
if(height == 0) height = 1;
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glViewport(0, 0, width, height);
gluPerspective(60.0f, 1.0 * width / height, 1.0f, 1000.0f);
glMatrixMode(GL_MODELVIEW);
}
void renderScene(void) {
glClearColor(0.7f, 0.7f, 0.7f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
changeSize(glutGet(GLUT_WINDOW_WIDTH), glutGet(GLUT_WINDOW_HEIGHT));
glLoadIdentity();
SceneCamera.Move(CameraDirection, elapsedTime);
SceneCamera.LookAt();
SceneAxis.DrawCameraAxisSystem(0.03f, 0.8f, SceneCamera.GetRotationAngles());
glutSwapBuffers();
}
Suggestions?
Rather than disable depth testing, you can just glClear(GL_DEPTH_BUFFER_BIT);
before you render your overlay. Then whatever depth information was there is gone, but the pixels are all still there. However, your overlay will still render appropriately.