bezier.c

来自「OpeNGL超级宝典源代码. OpeNGL超级宝典源代码.」· C语言 代码 · 共 126 行

// Bezier.c
// OpenGL SuperBible
// Demonstrates OpenGL evaluators to draw bezier curve
// Program by Richard S. Wright Jr.

#include "../../Common/OpenGLSB.h"	// System and OpenGL Stuff
#include "../../Common/GLTools.h"   // GLTools


// The number of control points for this curve
GLint nNumPoints = 4;

GLfloat ctrlPoints[4][3]= {{  -4.0f, 0.0f, 0.0f},	// End Point
							{ -6.0f, 4.0f, 0.0f},	// Control Point
							{  6.0f, -4.0f, 0.0f},	// Control Point
							{  4.0f, 0.0f, 0.0f }};	// End Point

// This function is used to superimpose the control points over the curve
void DrawPoints(void)
    {
    int i;	// Counting variable

    // Set point size larger to make more visible
    glPointSize(5.0f);

    // Loop through all control points for this example
    glBegin(GL_POINTS);
        for(i = 0; i < nNumPoints; i++)
           glVertex2fv(ctrlPoints[i]);
    glEnd();
    }



// Called to draw scene
void RenderScene(void)
    {
    int i;
    
    // Clear the window with current clearing color
    glClear(GL_COLOR_BUFFER_BIT);

    // Sets up the bezier
    // This actually only needs to be called once and could go in
    // the setup function
    glMap1f(GL_MAP1_VERTEX_3,	// Type of data generated
    0.0f,						// Lower u range
    100.0f,						// Upper u range
    3,							// Distance between points in the data
    nNumPoints,					// number of control points
    &ctrlPoints[0][0]);			// array of control points

    // Enable the evaluator
    glEnable(GL_MAP1_VERTEX_3);

	// Use a line strip to "connect-the-dots"
	glBegin(GL_LINE_STRIP);
		for(i = 0; i <= 100; i++)
			{
			// Evaluate the curve at this point
			glEvalCoord1f((GLfloat) i); 
            }
    glEnd();

    // Use higher level functions to map to a grid, then evaluate the
    // entire thing.
    // Put these two functions in to replace above loop

    // Map a grid of 100 points from 0 to 100
   //glMapGrid1d(100,0.0,100.0);

    // Evaluate the grid, using lines
    //glEvalMesh1(GL_LINE,0,100);

    // Draw the Control Points
    DrawPoints();

    // Flush drawing commands
    glutSwapBuffers();
    }

// This function does any needed initialization on the rendering
// context. 
void SetupRC()
    {
    // Clear Window to white
    glClearColor(1.0f, 1.0f, 1.0f, 1.0f );

    // Draw in Blue
    glColor3f(0.0f, 0.0f, 1.0f);	
    }

///////////////////////////////////////
// Set 2D Projection
void ChangeSize(int w, int h)
	{
	// Prevent a divide by zero
	if(h == 0)
		h = 1;

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

	gluOrtho2D(-10.0f, 10.0f, -10.0f, 10.0f);

	// Modelview matrix reset
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
	}

int main(int argc, char* argv[])
	{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(800, 600);
	glutCreateWindow("2D Bezier Curve");
	glutReshapeFunc(ChangeSize);
	glutDisplayFunc(RenderScene);
	SetupRC();
	glutMainLoop();

	return 0;
	}