triangle.c

OpeNGL超级宝典源代码. OpeNGL超级宝典源代码.

// Triangle.c
// OpenGL SuperBible, Chapter 4
// Demonstrates OpenGL Triangle Fans, backface culling, and depth testing
// Program by Richard S. Wright Jr.
#include "../../Common/OpenGLSB.h"	// System and OpenGL Stuff
#include <math.h>


// Define a constant for the value of PI
#define GL_PI 3.1415f

// Rotation amounts
static GLfloat xRot = 0.0f;
static GLfloat yRot = 0.0f;

// Flags for effects
// Flags for effects
int iCull = 0;
int iOutline = 0;
int iDepth = 0;

///////////////////////////////////////////////////////////////////////////////
// Reset flags as appropriate in response to menu selections
void ProcessMenu(int value)
	{
	switch(value)
		{
		case 1:
			iDepth = !iDepth;
			break;

		case 2:
			iCull = !iCull;
			break;

		case 3:
			iOutline = !iOutline;
		default:
			break;
		}

	glutPostRedisplay();
	}


// Called to draw scene   《OpenGL超级宝典》p87
void RenderScene(void)
	{
	GLfloat x,y,angle;  // Storage for coordinates and angles
	int iPivot = 1;		// Used to flag alternating colors

	// Clear the window and the depth buffer
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	// Turn culling on if flag is set
	if(iCull)
		glEnable(GL_CULL_FACE);
	else
		glDisable(GL_CULL_FACE);

	// Enable depth testing if flag is set
	if(iDepth)
		glEnable(GL_DEPTH_TEST);
	else
		glDisable(GL_DEPTH_TEST);

	// Draw back side as a polygon only, if flag is set
	if(iOutline)
		glPolygonMode(GL_BACK,GL_LINE);
	else
		glPolygonMode(GL_BACK,GL_FILL);
		

	// Save matrix state and do the rotation
	glPushMatrix();
	glRotatef(xRot, 1.0f, 0.0f, 0.0f);
	glRotatef(yRot, 0.0f, 1.0f, 0.0f);


	// Begin a triangle fan
	glBegin(GL_TRIANGLE_FAN);

	// Pinnacle of cone is shared vertex for fan, moved up Z axis
	// to produce a cone instead of a circle
	glVertex3f(0.0f, 0.0f, 75.0f);
	
	// Loop around in a circle and specify even points along the circle
	// as the vertices of the triangle fan
	for(angle = 0.0f; angle < (2.0f*GL_PI); angle += (GL_PI/8.0f))
		{
		// Calculate x and y position of the next vertex
		x = 50.0f*sin(angle);
		y = 50.0f*cos(angle);
	
		// Alternate color between red and green
		if((iPivot %2) == 0)
			glColor3f(0.0f, 1.0f, 0.0f);
		else
			glColor3f(1.0f, 0.0f, 0.0f);
			
		// Increment pivot to change color next time
		iPivot++;

		// Specify the next vertex for the triangle fan
		glVertex2f(x, y);
		}

	// Done drawing fan for cone
	glEnd();


	// Begin a new triangle fan to cover the bottom
	glBegin(GL_TRIANGLE_FAN);

	// Center of fan is at the origin
	glVertex2f(0.0f, 0.0f);
	for(angle = 0.0f; angle < (2.0f*GL_PI); angle += (GL_PI/8.0f))
		{
		// Calculate x and y position of the next vertex
		x = 50.0f*sin(angle);
		y = 50.0f*cos(angle);
	
		// Alternate color between red and green
		if((iPivot %2) == 0)
			glColor3f(0.0f, 1.0f, 0.0f);
		else
			glColor3f(1.0f, 0.0f, 0.0f);
			
		// Increment pivot to change color next time
		iPivot++;

		// Specify the next vertex for the triangle fan
		glVertex2f(x, y);
		}

	// Done drawing the fan that covers the bottom
	glEnd();

	// Restore transformations
	glPopMatrix();


	// Flush drawing commands
	glutSwapBuffers();
	}

// This function does any needed initialization on the rendering
// context. 
void SetupRC()
	{
	// Black background
	glClearColor(0.0f, 0.0f, 0.0f, 1.0f );

	// Set drawing color to green
	glColor3f(0.0f, 1.0f, 0.0f);

	// Set color shading model to flat
	glShadeModel(GL_FLAT);

	// Clock wise wound polygons are front facing, this is reversed
	// because we are using triangle fans
	glFrontFace(GL_CW);
	}

void SpecialKeys(int key, int x, int y)
	{
	if(key == GLUT_KEY_UP)
		xRot-= 5.0f;

	if(key == GLUT_KEY_DOWN)
		xRot += 5.0f;

	if(key == GLUT_KEY_LEFT)
		yRot -= 5.0f;

	if(key == GLUT_KEY_RIGHT)
		yRot += 5.0f;

	if(key > 356.0f)
		xRot = 0.0f;

	if(key < -1.0f)
		xRot = 355.0f;

	if(key > 356.0f)
		yRot = 0.0f;

	if(key < -1.0f)
		yRot = 355.0f;

	// Refresh the Window
	glutPostRedisplay();
	}


void ChangeSize(int w, int h)
	{
	GLfloat nRange = 100.0f;

	// Prevent a divide by zero
	if(h == 0)
		h = 1;

	// Set Viewport to window dimensions
    glViewport(0, 0, w, h);

	// Reset projection matrix stack
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();

	// Establish clipping volume (left, right, bottom, top, near, far)
    if (w <= h) 
		glOrtho (-nRange, nRange, -nRange*h/w, nRange*h/w, -nRange, nRange);
    else 
		glOrtho (-nRange*w/h, nRange*w/h, -nRange, nRange, -nRange, nRange);

	// Reset Model view matrix stack
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
	}

int main(int argc, char* argv[])
	{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
	glutCreateWindow("Triangle Culling Example");
	
	// Create the Menu
	glutCreateMenu(ProcessMenu);
	glutAddMenuEntry("Toggle depth test",1);
	glutAddMenuEntry("Toggle cull backface",2);
	glutAddMenuEntry("Toggle outline back",3);
	glutAttachMenu(GLUT_RIGHT_BUTTON);
	
	glutReshapeFunc(ChangeSize);
	glutSpecialFunc(SpecialKeys);
	glutDisplayFunc(RenderScene);
	SetupRC();
	glutMainLoop();

	return 0;
	}