[英]Mapping a texture in OpenGL
I am trying to map a texture to a simple quad for the first time, but all it won't render.我第一次尝试将纹理映射到一个简单的四边形,但它不会渲染。 I am using freeglut for the implementation, and the stb_image.h header to load the texture.
我正在使用 freeglut 进行实现,并使用 stb_image.h 标头来加载纹理。 The code:
编码:
#include <GL/glut.h>
#include <stb_image.h>
#include <iostream>
int ww = 500, wh = 500;
void display()
{
glClearColor(1.0, 1.0, 0.7, 1.0);
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_QUADS);
glEnable(GL_TEXTURE_2D);
glTexCoord2f(0.0, 0.0); glVertex3f(10,10,0);
glTexCoord2f(0.0, 1.0); glVertex3f(10,wh-10,0);
glTexCoord2f(1.0, 1.0); glVertex3f(ww-10,wh,0);
glTexCoord2f(1.0, 0.0); glVertex3f(ww-10,10,0);
glDisable(GL_TEXTURE_2D);
glEnd();
glFlush();
}
void myinit()
{
glViewport(0, 0, ww, wh);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0.0, (GLdouble)ww, 0.0, (GLdouble)wh);
glMatrixMode(GL_MODELVIEW);
unsigned int texture;
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
int width, height, nrChannels;
unsigned char* data = stbi_load("container.jpg", &width, &height, &nrChannels, 0);
if (data)
{
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);
}
else
{
std::cout << "Failed to load texture" << std::endl;
}
stbi_image_free(data);
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGBA);
glutInitWindowSize(ww, wh);
glutCreateWindow("texture-try");
glutDisplayFunc(display);
myinit();
glutMainLoop();
return 0;
}
It successfully loads the texture, but the quad appears just white.它成功加载了纹理,但四边形显示为白色。 What am I missing?
我错过了什么?
Edit:编辑:
I moved the glBegin(GL_QUADS);
我移动了
glBegin(GL_QUADS);
and glEnd();
和
glEnd();
inside the glEnable(GL_TEXTURE_2D);
在
glEnable(GL_TEXTURE_2D);
and glDisable(GL_TEXTURE_2D);
和
glDisable(GL_TEXTURE_2D);
commands as was suggested, but it still won't render the texture.建议的命令,但它仍然不会渲染纹理。
I also checked the glGetError
command, but it returns GL_NO_ERROR
.我还检查了
glGetError
命令,但它返回GL_NO_ERROR
。
From the OpenGL documentation for glBegin:从 glBegin 的 OpenGL 文档:
Only a subset of GL commands can be used between glBegin and glEnd.
在 glBegin 和 glEnd 之间只能使用 GL 命令的子集。 The commands are glVertex, glColor, glSecondaryColor, glIndex, glNormal, glFogCoord, glTexCoord, glMultiTexCoord, glVertexAttrib, glEvalCoord, glEvalPoint, glArrayElement, glMaterial, and glEdgeFlag.
这些命令是 glVertex、glColor、glSecondaryColor、glIndex、glNormal、glFogCoord、glTexCoord、glMultiTexCoord、glVertexAttrib、glEvalCoord、glEvalPoint、glArrayElement、glMaterial 和 glEdgeFlag。 Also, it is acceptable to use glCallList or glCallLists to execute display lists that include only the preceding commands.
此外,可以使用 glCallList 或 glCallLists 来执行仅包含上述命令的显示列表。 If any other GL command is executed between glBegin and glEnd, the error flag is set and the command is ignored.
如果在 glBegin 和 glEnd 之间执行了任何其他 GL 命令,则设置错误标志并忽略该命令。
In other words, you can't enable/disable texturing within a glBegin/glEnd block.换句话说,您不能在 glBegin/glEnd 块中启用/禁用纹理。
void display()
{
glClearColor(1.0, 1.0, 0.7, 1.0);
glClear(GL_COLOR_BUFFER_BIT);
// move to before glBegin
glEnable(GL_TEXTURE_2D);
glBegin(GL_QUADS);
glTexCoord2f(0.0, 0.0); glVertex3f(10,10,0);
glTexCoord2f(0.0, 1.0); glVertex3f(10,wh-10,0);
glTexCoord2f(1.0, 1.0); glVertex3f(ww-10,wh,0);
glTexCoord2f(1.0, 0.0); glVertex3f(ww-10,10,0);
glEnd();
// move to after glEnd
glDisable(GL_TEXTURE_2D);
glFlush();
}
Several things:几件事:
glBegin()
/ glEnd()
pair" issue;glBegin()
/ glEnd()
对中使用禁止的函数”问题; as of posting this hasn't been fixed in the question code.GL_LINEAR_MIPMAP_LINEAR
is being used without providing any mipmaps.GL_LINEAR_MIPMAP_LINEAR
而不提供任何 mipmap。 Drop to GL_LINEAR
or provide some mipmaps.GL_LINEAR
或提供一些 mipmap。3
to stbi_load()
's desired_channels
parameter (instead of the current 0
) to guarantee you get 3-channel image data instead of just assuming nrChannels
is 3
for all input images.3
传递给stbi_load()
的desired_channels
参数(而不是当前的0
)以保证您获得 3 通道图像数据,而不是仅仅假设所有输入图像的nrChannels
为3
。GL_RGB
with the default GL_UNPACK_ALIGNMENT
of 4
can result in wonky display if your image width isn't a nice multiple of 4 so drop that down to 1
via glPixelStorei(GL_UNPACK_ALIGNMENT, 1)
before calling glTexImage2D()
.GL_RGB
为4
的GL_UNPACK_ALIGNMENT
可能会导致显示不稳定,因此请在调用glTexImage2D()
之前通过glPixelStorei(GL_UNPACK_ALIGNMENT, 1)
将其降至1
。GLUT_DOUBLE
& glutSwapBuffers()
instead of using GLUT_SINGLE
and glFlush()
.GLUT_DOUBLE
和glutSwapBuffers()
而不是使用GLUT_SINGLE
和glFlush()
。 All together:全部一起:
#include <GL/glut.h>
#define STB_IMAGE_IMPLEMENTATION
#include <stb_image.h>
#include <iostream>
int ww = 500, wh = 500;
void display()
{
glClearColor(1.0, 1.0, 0.7, 1.0);
glClear(GL_COLOR_BUFFER_BIT);
glEnable(GL_TEXTURE_2D);
glBegin(GL_QUADS);
glTexCoord2f(0.0, 0.0); glVertex3f(10,10,0);
glTexCoord2f(0.0, 1.0); glVertex3f(10,wh-10,0);
glTexCoord2f(1.0, 1.0); glVertex3f(ww-10,wh,0);
glTexCoord2f(1.0, 0.0); glVertex3f(ww-10,10,0);
glEnd();
glDisable(GL_TEXTURE_2D);
glutSwapBuffers();
}
void myinit()
{
glViewport(0, 0, ww, wh);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0.0, (GLdouble)ww, 0.0, (GLdouble)wh);
glMatrixMode(GL_MODELVIEW);
unsigned int texture;
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
int width, height, nrChannels;
// https://commons.wikimedia.org/wiki/File:Container.JPG
unsigned char* data = stbi_load("container.jpg", &width, &height, &nrChannels, 3);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
if (data)
{
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);
}
else
{
std::cout << "Failed to load texture" << std::endl;
}
stbi_image_free(data);
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);
glutInitWindowSize(ww, wh);
glutCreateWindow("texture-try");
glutDisplayFunc(display);
myinit();
glutMainLoop();
return 0;
}
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