纹理的内部格式 [英] the internalformat of Texture
问题描述
void glTexImage2D(GLenum target,
GLint level,
GLint internalFormat,
GLsizei宽度,
GLsizei高度,
GLint边界,
GLenum格式,
GLenum类型,
常量GLvoid * data);
我知道参数的格式和类型描述了图像数据的格式和类型, t理解参数 internalFormat 。如何在应用程序中设置它的值?
例如,我创建了一个如下所示的纹理: glTexImage2D(GL_TEXTURE_2D,0,GL_LUMINANCE8,size,size,0,GL_LUMINANCE,GL_UNSIGNED_BYTE,buffer);
当我在我的GLSL着色器中使用纹理时,看起来我得到的值是在[0,1] .WHy之间,不应该介于[0,255]之间吗?
我的着色器代码的一部分是:
vec = EntryPoint + delta_dir *纹理(noiseTex,EntryPoint.xy * 32).x;
部分我的C ++代码:
<$ p (int i = 0; i
buffer [i] = 255.0 * rand()/(float)RAND_MAX; $ p>
}
glGenTextures(1,& noiseTex);
glActiveTexture(GL_TEXTURE0 + activeTexUnit);
glBindTexture(GL_TEXTURE_2D,noiseTex);
glTexImage2D(GL_TEXTURE_2D,0,GL_LUMINANCE8,size,size,
0,GL_LUMINANCE,GL_UNSIGNED_BYTE,buffer);
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_NEAREST);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_NEAREST);
格式
和 type
参数描述了作为像素传输操作。 internalformat
描述纹理的格式 格式 的。你告诉OpenGL你要让它看起来像X,而OpenGL将它存储在数据为Y的纹理中。 internalformat
是Y 。
$ b
GL_LUMINANCE8
内部格式表示一个标准化的无符号整数格式。这意味着数据在概念上是浮点数据,但是以标准化的整数形式存储为压缩方式。
对于这个问题,
表示您正在传递浮点数据或标准化整数数据( GL_LUMINANCE
的格式 type
表示它是标准化的整数数据)。当然,由于没有 GL_LUMINANCE_INTEGER
(这就是你如何传递 integer 数据,与整数内部格式一起使用),您无法真正使用像这样的亮度数据。
使用 GL_RED_INTEGER
作为格式和 GL_R8UI
作为内部格式,如果您真的需要纹理中的8位无符号整数。请注意,整数纹理支持需要OpenGL 3.x级硬件。
就是说, 不能 使用带有整数纹理的 sampler2D
。如果您使用的是使用无符号整数纹理格式的纹理,则 必须 使用 usampler2D
。
Look at the following OpenGL function:
void glTexImage2D(GLenum target,
GLint level,
GLint internalFormat,
GLsizei width,
GLsizei height,
GLint border,
GLenum format,
GLenum type,
const GLvoid * data);
I know the parameter format and type describe the format and type of the image data,but I don't understand the prameter internalFormat.How should I set its value in my application?
For example,I create a texture like this:
glTexImage2D(GL_TEXTURE_2D,0,GL_LUMINANCE8,size,size,0,GL_LUMINANCE,GL_UNSIGNED_BYTE,buffer);
When I aceess the texture in it in my GLSL shader,it seems that the value that I get is between [0,1].WHy?Shouldn't it between [0,255]?
Part of My shader code is :
vec = EntryPoint + delta_dir * texture(noiseTex,EntryPoint.xy * 32).x;
Part of my C++ Code :
for (int i = 0;i < temp;++i)
{
buffer[i] = 255.0 * rand() / (float)RAND_MAX;
}
glGenTextures(1,&noiseTex);
glActiveTexture(GL_TEXTURE0 + activeTexUnit);
glBindTexture(GL_TEXTURE_2D,noiseTex);
glTexImage2D(GL_TEXTURE_2D,0,GL_LUMINANCE8,size,size,
0,GL_LUMINANCE,GL_UNSIGNED_BYTE,buffer);
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_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
The format
and type
parameters describe the data you are passing to OpenGL as part of a pixel transfer operation. The internalformat
describes the format of the texture. You're telling OpenGL that you're giving it takes that looks like X, and OpenGL is to store it in a texture where the data is Y. The internalformat
is "Y".
The GL_LUMINANCE8
internal format represents a normalized unsigned integer format. This means that the data is conceptually floating-point, but stored in a normalized integer form as a means of compression.
For that matter, the format
of GL_LUMINANCE
says that you're passing either floating-point data or normalized integer data (the type
says that it's normalized integer data). Of course, since there's no GL_LUMINANCE_INTEGER
(which is how you say that you're passing integer data, to be used with integer internal formats), you can't really use luminance data like this.
Use GL_RED_INTEGER
for the format and GL_R8UI
for the internal format if you really want 8-bit unsigned integers in your texture. Note that integer texture support requires OpenGL 3.x-class hardware.
That being said, you cannot use sampler2D
with an integer texture. If you are using a texture that uses an unsigned integer texture format, you must use usampler2D
.
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