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[图形学] Chp18 OpenGL表面纹理函数

Posted on 2017-06-30 17:26  珍蜗蜗  阅读(399)  评论(0)  编辑  收藏  举报

　　以2D表面为例展示纹理贴图，用opengl设置一个2D纹理，颜色存储在32*32*3的数组中，对应的纹理坐标为0<=s, t<=1.0. 画出几个正方形表面，分别以GL_CLAMP(纹理坐标大于1或小于0都被规范到1和0)，GL_REPEAT（类似平铺，超过0或1的部分忽略整数位进行贴图），GL_MODULATE（纹理颜色与对象颜色相乘）, GL_REPLACE(纹理颜色替换对象颜色)几种形式进行贴图。

 

  1 #include <GLUT/GLUT.h>
  2 
  3 GLsizei winWidht = 500, winHeight = 500;
  4 
  5 void init (void)
  6 {
  7     glClearColor(1.0, 1.0, 1.0, 0.0);
  8     
  9     glMatrixMode(GL_PROJECTION);
 10     glLoadIdentity();
 11     gluOrtho2D(-5, 5, -5, 5);
 12 }
 13 
 14 void xyCoords (void)
 15 {
 16     glBegin(GL_LINES);
 17     glColor3f(0.0, 0.0, 0.0);
 18     glVertex2i(-10, 0);
 19     glVertex2i(10, 0);
 20     glVertex2i(0, -10);
 21     glVertex2i(0, 10);
 22     glEnd();
 23 }
 24 
 25 void lineTextureMapping (void)
 26 {
 27     GLint k;
 28     GLubyte texLine [16];
 29     
 30     for (k = 0; k <= 2; k +=2) {
 31         texLine [4*k] = 0;
 32         texLine [4*k+1] = 255;
 33         texLine [4*k+2] = 0;
 34         texLine [4*k+3] = 255;
 35     }
 36     
 37     for (k = 1; k <= 3; k +=2) {
 38         texLine [4*k] = 255;
 39         texLine [4*k+1] = 0;
 40         texLine [4*k+2] = 0;
 41         texLine [4*k+3] = 255;
 42     }
 43     
 44     glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
 45     glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
 46     
 47     glTexImage1D(GL_TEXTURE_1D, 0, GL_RGBA, 4, 0, GL_RGBA, GL_UNSIGNED_BYTE, texLine);
 48     glEnable(GL_TEXTURE_1D);
 49     
 50     glColor3f(1.0, 1.0, 1.0);
 51     glBegin(GL_LINES);
 52     glTexCoord1f(0.25);
 53     glVertex2f(-4.5, 4.0);
 54     glTexCoord1f(1.0);
 55     glVertex2f(-4.5, -4.0);
 56     glEnd();
 57     
 58     glDisable(GL_TEXTURE_1D);
 59 }
 60 
 61 void surfaceTextureMapping (void)
 62 {
 63     GLint k, j;
 64     GLubyte texArray [32][32][4];
 65     
 66     for (k = 0; k < 32; k++) {
 67         for (j = 0; j < 32; j++) {
 68             texArray [k][j][0] = 255 - k*j/4;
 69             texArray [k][j][1] = 128 + k*j/8;
 70             texArray [k][j][2] = 0;
 71             texArray [k][j][3] = 255;
 72         }
 73     }
 74     
 75     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
 76     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
 77     glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 32, 32, 0, GL_RGBA, GL_UNSIGNED_BYTE, texArray);
 78     glEnable(GL_TEXTURE_2D);
 79     
 80     glColor3f(0.5, 0.5, 0.5); // 与纹理值相乘，因此会发暗
 81     glBegin(GL_QUADS);
 82     glTexCoord2f(0.0, 0.0);
 83     glVertex2f(0.0, 0.0);
 84     glTexCoord2f(3.0, 0.0);
 85     glVertex2f(3.0, 0.0);
 86     glTexCoord2f(3.0, 3.0);
 87     glVertex2f(3.0, 3.0);
 88     glTexCoord2f(0.0, 3.0);
 89     glVertex2f(0.0, 3.0);
 90     glEnd();
 91     
 92     glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
 93     glColor3f(0.5, 0.5, 0.5); // 替换为纹理颜色，则不会像前一个图案那样发暗
 94     glBegin(GL_QUADS);
 95     glTexCoord2f(0.0, 0.0);
 96     glVertex2f(-4.0, -4.0);
 97     glTexCoord2f(1.0, 0.0);
 98     glVertex2f(-1.0, -4.0);
 99     glTexCoord2f(1.0, 1.0);
100     glVertex2f(-1.0, -1.0);
101     glTexCoord2f(0.0, 1.0);
102     glVertex2f(-4.0, -1.0);
103     glEnd();
104     glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
105     
106     // 不允许纹理坐标超过1，因此小于0的设为0，大于1的设为1
107     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
108     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
109     glColor3f(1.0, 1.0, 1.0);
110     glBegin(GL_QUADS);
111     glTexCoord2f(0.0, 0.0);
112     glVertex2f(-4.0, 0.0);
113     glTexCoord2f(2, 0.0);
114     glVertex2f(-1.0, 0.0);
115     glTexCoord2f(2, 2);
116     glVertex2f(-1.0, 3.0);
117     glTexCoord2f(0.0, 2);
118     glVertex2f(-4.0, 3.0);
119     glEnd();
120     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
121     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
122     
123     glDisable(GL_TEXTURE_2D);
124 }
125 
126 void displayFcn (void)
127 {
128     glClear(GL_COLOR_BUFFER_BIT);
129     
130 //    lineTextureMapping();
131     surfaceTextureMapping();
132     xyCoords();
133     
134     glFlush();
135 }
136 
137 void winReshapeFcn (GLint newWidth, GLint newHeight)
138 {
139     glViewport(0, 0, newWidth, newHeight);
140 }
141 
142 int main(int argc, char * argv[])
143 {
144     glutInit(&argc, argv);
145     glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
146     glutInitWindowSize(winWidht, winHeight);
147     glutInitWindowPosition(100, 100);
148     glutCreateWindow("texture mapping");
149     
150     init();
151     glutDisplayFunc(displayFcn);
152     glutReshapeFunc(winReshapeFcn);
153     glutMainLoop();
154     
155     return 0;
156 }
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