代码分析
3d纹理的配置要比2d纹理复杂一些
glPixelStorei
glPixelStorei(GL_UNPACK_ALIGNMENT, 1)
让字节对齐从默认的4字节对齐改成1字节对齐(选择1的话,无论图片本身是怎样都是绝对不会出问题的,以效率的牺牲为代价)
涉及到cpu把纹理传给gpu要按照像素的方式,这样提取出来就是整齐的rgba格式
PACK —— 把像素从一堆X的状态转变到规则的状态(把一堆泥土装载进一个花盆,把散散的货物装上货柜,或者把一堆各样的文件打包成一个rar压缩包,等等);
UNPACK —— 把像素从规则的状态转变到一堆X的状态(把花盆里的泥倒出来,把货柜中的货物卸载到盐田港,或者解压压缩包,等等)。
从本地内存向GPU的传输(UNPACK),包括各种glTexImage、glDrawPixel;从GPU到本地内存的传输(PACK),包括glGetTexImage、glReadPixel等
完整代码
#include <GL/glut.h>
#include <GL/glext.h>
#include <stdlib.h>
#include <stdio.h>
#ifdef GL_VERSION_1_2
#define iWidth 16
#define iHeight 16
#define iDepth 16
static GLubyte image[iDepth][iHeight][iWidth][3]; //深度,高度,宽度+3个颜色通道
static GLuint texName;
/* Create a 16x16x16x3 array with different color values in
* each array element [r, g, b]. Values range from 0 to 255.
*/
PFNGLTEXIMAGE3DPROC glTexImage3D; //定义一个glTexImage3D指针
void makeImage(void) //造纹理
{
int s, t, r;
for (s = 0; s < 16; s++)
for (t = 0; t < 16; t++)
for (r = 0; r < 16; r++) {
image[r][t][s][0] = (GLubyte) (s * 17);
image[r][t][s][1] = (GLubyte) (t * 17);
image[r][t][s][2] = (GLubyte) (r * 17);
}
}
void init(void)
{
glClearColor (0.0, 0.0, 0.0, 0.0);
glShadeModel(GL_FLAT); //两点之间的着色模式为片状,另一个参数可以写为,GL_SMOOTH这样绘制出来的就是渐变效果
//glShadeModel(GL_SMOOTH);
glEnable(GL_DEPTH_TEST); //启用深度测试
makeImage(); //产生纹理
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glGenTextures(1, &texName);
glBindTexture(GL_TEXTURE_3D, texName);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_T, GL_CLAMP);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_R, GL_CLAMP);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
//q是一个缩放因子,相当于顶点坐标中的w。实际应用在纹理读取中的坐标应该是s/q,t/q,r/q。默认情况下,q是1.0。通常情况下貌似没什么用,但是在一些产生纹理坐标的高级算法比如阴影贴图中
//s、t、r分别相当于普通坐标系中的x、y、z三个方向。分别对应glTexImage3D中的参数width、height、depth。
glTexImage3D = reinterpret_cast< PFNGLTEXIMAGE3DPROC>( ::wglGetProcAddress( "glTexImage3D") ); //使能glTexImage3D指针
glTexImage3D(GL_TEXTURE_3D, 0, GL_RGB, iWidth, iHeight,iDepth, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
glEnable(GL_TEXTURE_3D);
}
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glBegin(GL_QUADS);
glTexCoord3f(0.0, 0.0, 0.0); glVertex3f(-2.25, -1.0, 0.0);
glTexCoord3f(0.0, 1.0, 0.0); glVertex3f(-2.25, 1.0, 0.0);
glTexCoord3f(1.0, 1.0, 1.0); glVertex3f(-0.25, 1.0, 0.0);
glTexCoord3f(1.0, 0.0, 1.0); glVertex3f(-0.25, -1.0, 0.0);
glTexCoord3f(0.0, 0.0, 1.0); glVertex3f(0.25, -1.0, 0.0);
glTexCoord3f(0.0, 1.0, 1.0); glVertex3f(0.25, 1.0, 0.0);
glTexCoord3f(1.0, 1.0, 0.0); glVertex3f(2.25, 1.0, 0.0);
glTexCoord3f(1.0, 0.0, 0.0); glVertex3f(2.25, -1.0, 0.0);
glEnd();
glFlush();
}
void reshape(int w, int h)
{
glViewport(0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(60.0, (GLfloat) w/(GLfloat) h, 1.0, 30.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0, 0.0, -4.0);
}
void keyboard(unsigned char key, int x, int y)
{
switch (key) {
case 27:
exit(0);
break;
}
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(250, 250);
glutInitWindowPosition(100, 100);
glutCreateWindow(argv[0]);
init();
glutReshapeFunc(reshape);
glutDisplayFunc(display);
glutKeyboardFunc (keyboard);
glutMainLoop();
return 0;
}
#else
int main(int argc, char** argv)
{
fprintf (stderr, "This program demonstrates a feature which is not in OpenGL Version 1.0 or 1.1.\n");
fprintf (stderr, "If your implementation of OpenGL has the right extensions,\n");
fprintf (stderr, "you may be able to modify this program to make it run.\n");
return 0;
}
#endif
最终效果
效果图如下: