Solved: Opengl error | Experts Exchange

Infinity08

3/6/2011

>> What does this error mean?

Impossible to say without seeing more of the code.

But there's a good chance that Robot isn't an object.

Btw, this is not an OpenGL error, but a C++ error.

tango2009

3/7/2011

ASKER

I have posted the class below that creates the robot animated character.

#ifdef _WINDOWS
#include <windows.h>
#endif

//#include <gl/gl.h>
#include <gl/glut.h>

#include "Enemy.h"

Robot::Robot()
{
	armAngles[LEFT] = 0.0;
	armAngles[RIGHT] = 0.0;
	legAngles[LEFT] = 0.0;
	legAngles[RIGHT] = 0.0;

	armStates[LEFT] = FORWARD_STATE;
	armStates[RIGHT] = BACKWARD_STATE;

	legStates[LEFT] = FORWARD_STATE;
	legStates[RIGHT] = BACKWARD_STATE;
}

Robot::~Robot()
{
}

void Robot::DrawCube(float xPos, float yPos, float zPos)
{
	glPushMatrix();
		glTranslatef(xPos, yPos, zPos);
		glBegin(GL_POLYGON);
			glVertex3f(0.0f, 0.0f, 0.0f);	// top face
			glVertex3f(0.0f, 0.0f, -1.0f);
			glVertex3f(-1.0f, 0.0f, -1.0f);
			glVertex3f(-1.0f, 0.0f, 0.0f);
			glVertex3f(0.0f, 0.0f, 0.0f);	// front face
			glVertex3f(-1.0f, 0.0f, 0.0f);
			glVertex3f(-1.0f, -1.0f, 0.0f);
			glVertex3f(0.0f, -1.0f, 0.0f);
			glVertex3f(0.0f, 0.0f, 0.0f);	// right face
			glVertex3f(0.0f, -1.0f, 0.0f);
			glVertex3f(0.0f, -1.0f, -1.0f);
			glVertex3f(0.0f, 0.0f, -1.0f);
			glVertex3f(-1.0f, 0.0f, 0.0f);	// left face
			glVertex3f(-1.0f, 0.0f, -1.0f);
			glVertex3f(-1.0f, -1.0f, -1.0f);
			glVertex3f(-1.0f, -1.0f, 0.0f);
			glVertex3f(0.0f, 0.0f, 0.0f);	// bottom face
			glVertex3f(0.0f, -1.0f, -1.0f);
			glVertex3f(-1.0f, -1.0f, -1.0f);
			glVertex3f(-1.0f, -1.0f, 0.0f);
			glVertex3f(0.0f, 0.0f, 0.0f);	// back face
			glVertex3f(-1.0f, 0.0f, -1.0f);
			glVertex3f(-1.0f, -1.0f, -1.0f);
			glVertex3f(0.0f, -1.0f, -1.0f);
		glEnd();
	glPopMatrix();
}

void Robot::DrawArm(float xPos, float yPos, float zPos)
{
	glPushMatrix();
		glColor3f(1.0f, 0.0f, 0.0f);	// red
		glTranslatef(xPos, yPos, zPos);
		glScalef(1.0f, 4.0f, 1.0f);		// arm is a 1x4x1 cube
		DrawCube(0.0f, 0.0f, 0.0f);
	glPopMatrix();
}

void Robot::DrawHead(float xPos, float yPos, float zPos)
{
	glPushMatrix();
		glColor3f(1.0f, 1.0f, 1.0f);	// white
		glTranslatef(xPos, yPos, zPos);
		glScalef(2.0f, 2.0f, 2.0f);		// head is a 2x2x2 cube
		DrawCube(0.0f, 0.0f, 0.0f);
	glPopMatrix();
}

void Robot::DrawTorso(float xPos, float yPos, float zPos)
{
	glPushMatrix();
		glColor3f(0.0f, 0.0f, 1.0f);	// blue
		glTranslatef(xPos, yPos, zPos);
		glScalef(3.0f, 5.0f, 2.0f);		// torso is a 3x5x2 cube
		DrawCube(0.0f, 0.0f, 0.0f);
	glPopMatrix();
}

void Robot::DrawLeg(float xPos, float yPos, float zPos)
{
	glPushMatrix();
		glTranslatef(xPos, yPos, zPos);
		
		// draw the foot
		glPushMatrix();
			glTranslatef(0.0f, -0.5f, 0.0f);
			DrawFoot(0.0f, -5.0f, 0.0f);
		glPopMatrix();		
		
		glScalef(1.0f, 5.0f, 1.0f);		// leg is a 1x5x1 cube
		glColor3f(1.0f, 1.0f, 0.0f);	// yellow
		DrawCube(0.0f, 0.0f, 0.0f);
	glPopMatrix();
}

void Robot::DrawFoot(float xPos, float yPos, float zPos)
{
	glPushMatrix();
		glColor3f(1.0f, 1.0f, 1.0f);
		glTranslatef(xPos, yPos, zPos);
		glScalef(1.0f, 0.5f, 3.0f);
		DrawCube(0.0f, 0.0f, 0.0f);
	glPopMatrix();
}

void Robot::DrawRobot(float xPos, float yPos, float zPos)
{
	glPushMatrix();	
		glTranslatef(xPos, yPos, zPos);	// draw robot at desired coordinates

		// draw head and torso parts
		DrawHead(1.0f, 2.0f, 0.0f);		
		DrawTorso(1.5f, 0.0f, 0.0f);

		// move the left arm away from the torso and rotate it to give "walking" effect
		glPushMatrix();
			glTranslatef(0.0f, -0.5f, 0.0f);
			glRotatef(armAngles[LEFT], 1.0f, 0.0f, 0.0f);
			DrawArm(2.5f, 0.0f, -0.5f);
		glPopMatrix();

		// move the right arm away from the torso and rotate it to give "walking" effect
		glPushMatrix();
			glTranslatef(0.0f, -0.5f, 0.0f);
			glRotatef(armAngles[RIGHT], 1.0f, 0.0f, 0.0f);
			DrawArm(-1.5f, 0.0f, -0.5f);
		glPopMatrix();

		// move the left leg away from the torso and rotate it to give "walking" effect
		glPushMatrix();					
			glTranslatef(0.0f, -0.5f, 0.0f);
			glRotatef(legAngles[LEFT], 1.0f, 0.0f, 0.0f);
			DrawLeg(-0.5f, -5.0f, -0.5f);
		glPopMatrix();

		// move the right leg away from the torso and rotate it to give "walking" effect
		glPushMatrix();
			glTranslatef(0.0f, -0.5f, 0.0f);
			glRotatef(legAngles[RIGHT], 1.0f, 0.0f, 0.0f);
			DrawLeg(1.5f, -5.0f, -0.5f);
		glPopMatrix();

	glPopMatrix();	// pop back to original coordinate system
}

void Robot::Prepare(float dt)
{
	// if leg is moving forward, increase angle, else decrease angle
	for (char side = 0; side < 2; side++)
	{
		// arms
		if (armStates[side] == FORWARD_STATE)
			armAngles[side] += 20.0f * dt;
		else
			armAngles[side] -= 20.0f * dt;

		// change state if exceeding angles
		if (armAngles[side] >= 15.0f)
			armStates[side] = BACKWARD_STATE;
		else if (armAngles[side] <= -15.0f)
			armStates[side] = FORWARD_STATE;

		// legs
		if (legStates[side] == FORWARD_STATE)
			legAngles[side] += 20.0f * dt;
		else
			legAngles[side] -= 20.0f * dt;

		// change state if exceeding angles
		if (legAngles[side] >= 15.0f)
			legStates[side] = BACKWARD_STATE;
		else if (legAngles[side] <= -15.0f)
			legStates[side] = FORWARD_STATE;		
	}
}

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Infinity08

3/7/2011

So, Robot is a type, not an object.

You need to call the DrawRobot method from an instance of the Robot type.

You might want to read up on how to use classes in C++ :

http://www.cplusplus.com/doc/tutorial/classes/
http://www.cplusplus.com/doc/tutorial/classes2/

tango2009

3/13/2011

ASKER

This is how I am using my class now.

Robot enemy;

enemy.DrawRobot(1.0f,0.0f,0.0f);

One more question is there a way I can draw these at random around my world?