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3D Hell

Started by Ethereal Darkness Nov 13, 2001 at 3:20 PM 2 replies 500+ views

Original Post

Nov 13, 2001 at 3:20 PM

hey all, im working on building a 3d engine/library and the one part of it that has seemed to stump me is 3d hierarchial rotation, i.e. you rotate your shoulder and your forarm and hand follows i have come up with a way to do it... rotate self->rotate joints below it using the rotation origin of the first object. the idea works well... but i think the rotations im doing are messed up, so i was wondering if anyone could point me in the direction of a turoial or some information on doing 3d hierarchial rotations using software only *no graphics libraries or other engines* thanks=)

Kylotan

Nov 14, 2001 at 5:58 PM

I''m no 3D programmer, but surely if you just define your objects in relation to the object it is attached to, then you only need to transform one object and all the others are automatically transformed as a result...

Floppy

Nov 14, 2001 at 6:32 PM

Kylotan is right assuming that you do position your different objects in relation to some central object. I have done things like this for robot demos, here is a quick snippet. It''s in OpenGL and if you don''t understand push and pop techniques it''s probably hard to understand. Forward Kinematics is also something to look into for other types of physics simulations. I think there is a good tutorial somewhere on this website: OpenGL Effects

  
//  This function calls the function to draw the rest of the robot

void GLMain::DrawRobot()
{	
	glPushMatrix();

		glPushMatrix();
	
			//  Rotate bust

			glRotatef(bustXAngle, 1.0f, 0.0f, 0.0f);
			glRotatef(bustYAngle, 0.0f, 1.0f, 0.0f);

			//  Draw bust

			DrawBust();

			//  Draw head

			DrawHead();

			glPushMatrix();

				glTranslatef(-6.5f, 0.0f, 0.0f);

				//  Rotate left arm

				glRotatef(leftArmAngle, 1.0f, 0.0f, 0.0f);

				//  Draw left arm

				DrawArm();

				glPushMatrix();

					glTranslatef(0.0f, -4.5f, 0.0f);

					//  Rotate left forearm

					glRotatef(leftForeArmAngle, 1.0f, 0.0f, 0.0f);

					//  Draw left forearm

					DrawForeArm();

				glPopMatrix();
				
			glPopMatrix();
			
			glPushMatrix();

				glTranslatef(6.5f, 0.0f, 0.0f);

				//  Rotate right arm

				glRotatef(rightArmAngle, 1.0f, 0.0f, 0.0f);	

				//  Draw right arm

				DrawArm();

				glPushMatrix();

					glTranslatef(0.0f, -4.5f, 0.0f);

					//  Rotate right forearm

					glRotatef(rightForeArmAngle, 1.0f, 0.0f, 0.0f);

					//  Draw right forearm

					DrawForeArm();

				glPopMatrix();

			glPopMatrix();

				//  Draw Pelvis

				DrawPelvis();

			glPushMatrix();
				
				glTranslatef(-1.5f, -6.1f, 0.0f);

				//  Rotate left thigh

				glRotatef(leftThighAngle, 1.0f, 0.0f, 0.0f);

				//  Draw left thigh

				DrawThigh();
				
				glPushMatrix();

					glTranslatef(0.0f, -5.3f, 0.0f);

					//  Rotate left leg

					glRotatef(leftLegAngle, 1.0f, 0.0f, 0.0f);

					//  Draw the left leg

					DrawLeg();

				glPopMatrix();

			glPopMatrix();

			glPushMatrix();
				
				glTranslatef(1.5f, -6.1f, 0.0f);

				//  Rotate right thigh

				glRotatef(rightThighAngle, 1.0f, 0.0f, 0.0f);

				//  Draw right thigh

				DrawThigh();

				glPushMatrix();

					glTranslatef(0.0f, -5.3f, 0.0f);

					//  Rotate left leg

					glRotatef(rightLegAngle, 1.0f, 0.0f, 0.0f);

					//  Draw the left leg

					DrawLeg();

				glPopMatrix();

			glPopMatrix();
				
		glPopMatrix();

	glPopMatrix();
}

Well, maybe that wasn''t all that short, but you get the idea right? good!

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