任何人都可以使用 opengl 在 c 中给我一个简短的代码示例，其中单击两个不同的方 block 会改变它们的颜色？

Question

任何人都可以使用 opengl 在 c 中给我一个简短的代码示例，其中单击两个不同的方块会改变它们的颜色？我特别想知道如何检测鼠标点击发生在特定基元上。

Answer 1

这是一个 GL selection-mode example

/* Copyright (c) Mark J. Kilgard, 1994. */

/**
* (c) Copyright 1993, Silicon Graphics, Inc.
* ALL RIGHTS RESERVED 
* Permission to use, copy, modify, and distribute this software for 
* any purpose and without fee is hereby granted, provided that the above
* copyright notice appear in all copies and that both the copyright notice
* and this permission notice appear in supporting documentation, and that 
* the name of Silicon Graphics, Inc. not be used in advertising
* or publicity pertaining to distribution of the software without specific,
* written prior permission. 
*
* THE MATERIAL EMBODIED ON THIS SOFTWARE IS PROVIDED TO YOU "AS-IS"
* AND WITHOUT WARRANTY OF ANY KIND, EXPRESS, IMPLIED OR OTHERWISE,
* INCLUDING WITHOUT LIMITATION, ANY WARRANTY OF MERCHANTABILITY OR
* FITNESS FOR A PARTICULAR PURPOSE.  IN NO EVENT SHALL SILICON
* GRAPHICS, INC.  BE LIABLE TO YOU OR ANYONE ELSE FOR ANY DIRECT,
* SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY
* KIND, OR ANY DAMAGES WHATSOEVER, INCLUDING WITHOUT LIMITATION,
* LOSS OF PROFIT, LOSS OF USE, SAVINGS OR REVENUE, OR THE CLAIMS OF
* THIRD PARTIES, WHETHER OR NOT SILICON GRAPHICS, INC.  HAS BEEN
* ADVISED OF THE POSSIBILITY OF SUCH LOSS, HOWEVER CAUSED AND ON
* ANY THEORY OF LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE
* POSSESSION, USE OR PERFORMANCE OF THIS SOFTWARE.
* 
* US Government Users Restricted Rights 
* Use, duplication, or disclosure by the Government is subject to
* restrictions set forth in FAR 52.227.19(c)(2) or subparagraph
* (c)(1)(ii) of the Rights in Technical Data and Computer Software
* clause at DFARS 252.227-7013 and/or in similar or successor
* clauses in the FAR or the DOD or NASA FAR Supplement.
* Unpublished-- rights reserved under the copyright laws of the
* United States.  Contractor/manufacturer is Silicon Graphics,
* Inc., 2011 N.  Shoreline Blvd., Mountain View, CA 94039-7311.
*
* OpenGL(TM) is a trademark of Silicon Graphics, Inc.
*/

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include <time.h>
#include <GL/glut.h>

#define MAXOBJS 10000
#define MAXSELECT 100
#define MAXFEED 300
#define SOLID 1
#define LINE 2
#define POINT 3

GLint windW = 300, windH = 300;

GLuint selectBuf[MAXSELECT];
GLfloat feedBuf[MAXFEED];
GLint vp[4];
float zRotation = 90.0;
float zoom = 1.0;
GLint objectCount;
GLint numObjects;
struct object {
    float v1[2];
    float v2[2];
    float v3[2];
    float color[3];
} objects[MAXOBJS];
GLenum linePoly = GL_FALSE;

static void InitObjects(GLint num)
{
    GLint i;
    float x, y;

    if (num > MAXOBJS) {
        num = MAXOBJS;
    }
    if (num < 1) {
        num = 1;
    }
    objectCount = num;

    srand((unsigned int) time(NULL));
    for (i = 0; i < num; i++) {
        x = (rand() % 300) - 150;
        y = (rand() % 300) - 150;

        objects[i].v1[0] = x + (rand() % 50) - 25;
        objects[i].v2[0] = x + (rand() % 50) - 25;
        objects[i].v3[0] = x + (rand() % 50) - 25;
        objects[i].v1[1] = y + (rand() % 50) - 25;
        objects[i].v2[1] = y + (rand() % 50) - 25;
        objects[i].v3[1] = y + (rand() % 50) - 25;
        objects[i].color[0] = ((rand() % 100) + 50) / 150.0;
        objects[i].color[1] = ((rand() % 100) + 50) / 150.0;
        objects[i].color[2] = ((rand() % 100) + 50) / 150.0;
    }
}

static void Init(void)
{
    numObjects = 10;
    InitObjects(numObjects);
}

static void Reshape(int width, int height)
{
    windW = width;
    windH = height;
    glViewport(0, 0, windW, windH);
    glGetIntegerv(GL_VIEWPORT, vp);
}

static void Render(GLenum mode)
{
    GLint i;

    for (i = 0; i < objectCount; i++) {
        if (mode == GL_SELECT) {
            glLoadName(i);
        }
        glColor3fv(objects[i].color);
        glBegin(GL_POLYGON);
        glVertex2fv(objects[i].v1);
        glVertex2fv(objects[i].v2);
        glVertex2fv(objects[i].v3);
        glEnd();
    }
}

static GLint DoSelect(GLint x, GLint y)
{
    GLint hits;

    glSelectBuffer(MAXSELECT, selectBuf);
    glRenderMode(GL_SELECT);
    glInitNames();
    glPushName(~0);

    glPushMatrix();

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPickMatrix(x, windH - y, 4, 4, vp);
    gluOrtho2D(-175, 175, -175, 175);
    glMatrixMode(GL_MODELVIEW);

    glClearColor(0.0, 0.0, 0.0, 0.0);
    glClear(GL_COLOR_BUFFER_BIT);

    glScalef(zoom, zoom, zoom);
    glRotatef(zRotation, 0, 0, 1);

    Render(GL_SELECT);

    glPopMatrix();

    hits = glRenderMode(GL_RENDER);
    if (hits <= 0) {
        return -1;
    }
    return selectBuf[(hits - 1) * 4 + 3];
}

static void RecolorTri(GLint h)
{
    objects[h].color[0] = ((rand() % 100) + 50) / 150.0;
    objects[h].color[1] = ((rand() % 100) + 50) / 150.0;
    objects[h].color[2] = ((rand() % 100) + 50) / 150.0;
}

static void DeleteTri(GLint h)
{
    objects[h] = objects[objectCount - 1];
    objectCount--;
}

static void GrowTri(GLint h)
{
    float v[2];
    float *oldV;
    GLint i;

    v[0] = objects[h].v1[0] + objects[h].v2[0] + objects[h].v3[0];
    v[1] = objects[h].v1[1] + objects[h].v2[1] + objects[h].v3[1];
    v[0] /= 3;
    v[1] /= 3;

    for (i = 0; i < 3; i++) {
        switch (i) {
case 0:
    oldV = objects[h].v1;
    break;
case 1:
    oldV = objects[h].v2;
    break;
case 2:
    oldV = objects[h].v3;
    break;
        }
        oldV[0] = 1.5 * (oldV[0] - v[0]) + v[0];
        oldV[1] = 1.5 * (oldV[1] - v[1]) + v[1];
    }
}

static void Mouse(int button, int state, int mouseX, int mouseY)
{
    GLint hit;

    if (state == GLUT_DOWN) {
        hit = DoSelect((GLint) mouseX, (GLint) mouseY);
        if (hit != -1) {
            if (button == GLUT_LEFT_BUTTON) {
                RecolorTri(hit);
            } else if (button == GLUT_MIDDLE_BUTTON) {
                GrowTri(hit);
            } else if (button == GLUT_RIGHT_BUTTON) {
                DeleteTri(hit);
            }
            glutPostRedisplay();
        }
    }
}

static void Draw(void)
{
    glPushMatrix();
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(-175, 175, -175, 175);
    glMatrixMode(GL_MODELVIEW);
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glClear(GL_COLOR_BUFFER_BIT);
    glScalef(zoom, zoom, zoom);
    glRotatef(zRotation, 0, 0, 1);
    Render(GL_RENDER);
    glPopMatrix();
    glutSwapBuffers();
}

static void DumpFeedbackVert(GLint * i, GLint n)
{
    GLint index;

    index = *i;
    if (index + 7 > n) {
        *i = n;
        printf("  ???\n");
        return;
    }
    printf("  (%g %g %g), color = (%4.2f %4.2f %4.2f)\n",
        feedBuf[index],
        feedBuf[index + 1],
        feedBuf[index + 2],
        feedBuf[index + 3],
        feedBuf[index + 4],
        feedBuf[index + 5]);
    index += 7;
    *i = index;
}

static void DrawFeedback(GLint n)
{
    GLint i;
    GLint verts;

    printf("Feedback results (%d floats):\n", n);
    for (i = 0; i < n; i++) {
        switch ((GLint) feedBuf[i]) {
case GL_POLYGON_TOKEN:
    printf("Polygon");
    i++;
    if (i < n) {
        verts = (GLint) feedBuf[i];
        i++;
        printf(": %d vertices", verts);
    } else {
        verts = 0;
    }
    printf("\n");
    while (verts) {
        DumpFeedbackVert(&i, n);
        verts--;
    }
    i--;
    break;
case GL_LINE_TOKEN:
    printf("Line:\n");
    i++;
    DumpFeedbackVert(&i, n);
    DumpFeedbackVert(&i, n);
    i--;
    break;
case GL_LINE_RESET_TOKEN:
    printf("Line Reset:\n");
    i++;
    DumpFeedbackVert(&i, n);
    DumpFeedbackVert(&i, n);
    i--;
    break;
default:
    printf("%9.2f\n", feedBuf[i]);
    break;
        }
    }
    if (i == MAXFEED) {
        printf("...\n");
    }
    printf("\n");
}

static void DoFeedback(void)
{
    GLint x;

    glFeedbackBuffer(MAXFEED, GL_3D_COLOR, feedBuf);
    (void) glRenderMode(GL_FEEDBACK);

    glPushMatrix();

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(-175, 175, -175, 175);
    glMatrixMode(GL_MODELVIEW);

    glClearColor(0.0, 0.0, 0.0, 0.0);
    glClear(GL_COLOR_BUFFER_BIT);

    glScalef(zoom, zoom, zoom);
    glRotatef(zRotation, 0, 0, 1);

    Render(GL_FEEDBACK);

    glPopMatrix();

    x = glRenderMode(GL_RENDER);
    if (x == -1) {
        x = MAXFEED;
    }
    DrawFeedback((GLint) x);
}

static void Key(unsigned char key, int x, int y)
{

    switch (key) {
case 'z':
    zoom /= 0.75;
    glutPostRedisplay();
    break;
case 'Z':
    zoom *= 0.75;
    glutPostRedisplay();
    break;
case 'f':
    DoFeedback();
    glutPostRedisplay();
    break;
case 'l':
    linePoly = !linePoly;
    if (linePoly) {
        glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
    } else {
        glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
    }
    glutPostRedisplay();
    break;
case 27:
    exit(0);
    }
}

static void SpecialKey(int key, int x, int y)
{

    switch (key) {
case GLUT_KEY_LEFT:
    zRotation += 0.5;
    glutPostRedisplay();
    break;
case GLUT_KEY_RIGHT:
    zRotation -= 0.5;
    glutPostRedisplay();
    break;
    }
}

int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
    glutCreateWindow("Select Test");
    Init();
    glutReshapeFunc(Reshape);
    glutKeyboardFunc(Key);
    glutSpecialFunc(SpecialKey);
    glutMouseFunc(Mouse);
    glutDisplayFunc(Draw);
    glutMainLoop();
    return 0;             /* ANSI C requires main to return int. */
}

该程序是 some other GLUT examples 的一部分.

GL 选择缓冲区已经过时且已损坏，但您最好使用颜色回读选择或一些与几何表示集成的 CPU 端“光线转换”系统。