OpenGL Superbible (2nd Edition)/OpenGL SuperBible e2.iso/book/Chap04/Triangle/Triangle.c

C/C++ Source or Header | 1999-08-10 | 5.2 KB | 247 lines

// Triangle.c
// OpenGL SuperBible, Chapter 4
// Demonstrates OpenGL Triangle Fans, backface culling, and depth testing
// Program by Richard S. Wright Jr.

#include <windows.h>
#include <gl/gl.h>
#include <gl/glu.h>
#include <gl/glut.h>
#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
BOOL bCull = FALSE;
BOOL bOutline = FALSE;
BOOL bDepth = FALSE;

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

        case 2:
            bCull = !bCull;
            break;

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

    glutPostRedisplay();
    }


// Called to draw scene
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(bCull)
        glEnable(GL_CULL_FACE);
    else
        glDisable(GL_CULL_FACE);

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

    // Draw back side as a polygon only, if flag is set
    if(bOutline)
        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;
    }