如何使用textureLod()对GLSL中的MIP级别进行采样？
据我所知，mipmap LOD只能通过顶点着色器“显式*”访问(尽管不确定420版是否支持它，因为大多数文档已经过时)。其次，您需要通过设置纹理参数来定义mipmap的细节层次，如GL_纹理_MAX_LEVEL和GL_TEXTURE_BASE_LEVEL**。
在我的代码中，我在调用glCompressedTexImage2D后定义了这些纹理参数：
glTexParameteri(texture_type, GL_TEXTURE_MIN_FILTER, min_filter);
glTexParameteri(texture_type, GL_TEXTURE_MAG_FILTER, mag_filter);
glTexParameteri(texture_type, GL_TEXTURE_MAX_LEVEL, 9);
glTexParameteri(texture_type, GL_TEXTURE_BASE_LEVEL, 0);
glTexParameteri(texture_type, GL_TEXTURE_MAG_FILTER, GL_LINEAR_MIPMAP_LINEAR);
glTexParameteri(texture_type, GL_TEXTURE_WRAP_S, wrap_s);
glTexParameteri(texture_type, GL_TEXTURE_WRAP_T, wrap_t);接下来，我为每个绑定每个纹理样本(类型，如反照率贴图等)使用此代码：
glActiveTexture(GL_TEXTURE0 + unit); // Set active texture type
glBindTexture(GL_TEXTURE_2D, id); // Bind the texture object最后，下面是我的着色器代码：
顶点：
# version 420 core
out vec3 _texcoord;
out vec4 _albedo_lod;
uniform sampler2D albedo; // Albedo and specular map
void main()
{
_texcoord = texcoord;
_albedo_lod = textureLod(albedo, vec2(_texcoord.st), 2.0);
}使用附加的片段：
# version 420 core
layout(location = 0) out vec4 gAlbedo; // Albedo texel colour
in vec3 _texcoord;
in vec4 _albedo_lod;
void main()
{
gAlbedo = _albedo_lod; // Assign albedo
}现在，由于某种原因，无论我输入什么LOD值，结果总是这样：
似乎是最后一个MIP级别(不管我输入了什么值)。请记住，我将10个MIP级别打包为一个**.dds文件。然而，当我通过纹理参数GL_TEXTURE_BASE_LEVEL**手动设置基本MIP级别时，它起作用了。
因此，总而言之，为什么它不能使用textureLod在GLSL中采样正确的MIP级别？这在版本420中是否有些过时？
**EDIT：**DDS文件加载代码如下：
// This function imports a dds file and returns the dds data as a struct
inline GLuint LoadDds(std::vector<std::string> file, size_t &img_width, size_t &img_height, size_t &num_mips, GLvoid* data, GLint wrap_s, GLint wrap_t, GLint min_filter, GLint mag_filter, size_t texture_type, bool anistropic_filtering)
{
// Create one OpenGL texture
GLuint textureID;
glGenTextures(1, &textureID);
// "Bind" the newly created texture : all future texture functions will modify this texture
glBindTexture(texture_type, textureID);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
for (unsigned int i = 0; i < file.size(); i++) // For each image...
{
FILE *fp;
unsigned char header[124];
unsigned int height;
unsigned int width;
unsigned int linearSize;
unsigned int mipMapCount;
unsigned int fourCC;
unsigned int components;
unsigned int format;
unsigned int bufsize;
unsigned char* buffer;
/* try to open the file */
errno_t err;
err = fopen_s(&fp, file[i].c_str(), "rb");
if (fp == NULL)
return 0;
/* verify the type of file */
char filecode[4];
fread(filecode, 1, 4, fp);
if (strncmp(filecode, "DDS ", 4) != 0)
{
fclose(fp);
return 0;
}
/* get the surface desc */
fread(&header, 124, 1, fp);
height = *(unsigned int*)&(header[8]);
width = *(unsigned int*)&(header[12]);
linearSize = *(unsigned int*)&(header[16]);
mipMapCount = *(unsigned int*)&(header[24]);
fourCC = *(unsigned int*)&(header[80]);
bufsize = mipMapCount > 1 ? linearSize * 2 : linearSize;
buffer = (unsigned char*)malloc(bufsize * sizeof(unsigned char));
fread(buffer, 1, bufsize, fp);
/* close the file pointer */
fclose(fp);
components = (fourCC == FOURCC_DXT1) ? 3 : 4;
switch (fourCC)
{
case FOURCC_DXT1:
format = GL_COMPRESSED_RGBA_S3TC_DXT1_EXT;
break;
case FOURCC_DXT3:
format = GL_COMPRESSED_RGBA_S3TC_DXT3_EXT;
break;
case FOURCC_DXT5:
format = GL_COMPRESSED_RGBA_S3TC_DXT5_EXT;
break;
default:
free(buffer);
return 0;
}
unsigned int blockSize = (format == GL_COMPRESSED_RGBA_S3TC_DXT1_EXT) ? 8 : 16;
unsigned int offset = 0;
for (unsigned int level = 0; level < mipMapCount && (width || height); ++level)
{
unsigned int size = ((width + 3) / 4) * ((height + 3) / 4) * blockSize;
glCompressedTexImage2D(texture_type != GL_TEXTURE_CUBE_MAP ? GL_TEXTURE_2D : GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, level, format, width, height,
0, size, buffer + offset);
if ((level < 1) && (i < 1)) // Only assign input variable values from first image
{
img_width = width; // Assign texture width
img_height = height; // Assign texture height
data = buffer; // Assign buffer data
num_mips = mipMapCount; // Assign number of mips
}
offset += size;
width /= 2;
height /= 2;
}
if (anistropic_filtering) // If anistropic_filtering is true...
{
GLfloat f_largest; // A contianer for storing the amount of texels in view for anistropic filtering
glGetFloatv(GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT, &f_largest); // Query the amount of texels for calculation
glTexParameterf(texture_type, GL_TEXTURE_MAX_ANISOTROPY_EXT, f_largest); // Apply filter to texture
}
if (!mipMapCount)
glGenerateMipmap(texture_type); // Generate mipmap
free(buffer); // Free buffers from memory
}
// Parameters
glTexParameteri(texture_type, GL_TEXTURE_MIN_FILTER, min_filter);
glTexParameteri(texture_type, GL_TEXTURE_MAG_FILTER, mag_filter);
glTexParameteri(texture_type, GL_GENERATE_MIPMAP, GL_TRUE);
glTexParameteri(texture_type, GL_TEXTURE_MAX_LEVEL, 9);
glTexParameteri(texture_type, GL_TEXTURE_BASE_LEVEL, 0);
glTexParameteri(texture_type, GL_TEXTURE_MAG_FILTER, GL_LINEAR_MIPMAP_LINEAR);
glTexParameteri(texture_type, GL_TEXTURE_WRAP_S, wrap_s);
glTexParameteri(texture_type, GL_TEXTURE_WRAP_T, wrap_t);
// Set additional cubemap parameters
if (texture_type == GL_TEXTURE_CUBE_MAP)
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R, wrap_s);
return textureID; // Return texture id
}下面是使用NVIDIA的DDS插件生成的每个mipmap级别的图像：
2条答案
按热度按时间tkclm6bt1#
由于逐顶点采样，这似乎正是预期的行为。
你说MIP级别参数没有影响，但从我所能看到的，只有当像素密度低于顶点密度并且值开始平均时，差异才应该是明显的。然而，如果你不存储整个mipchain，这可能永远不会发生，因为最低的分辨率可能仍然有足够的清晰度(我真的不能从屏幕截图中分辨出来，我只能猜测模型的镶嵌)。
但是，因为您是手动生成mipchain的，所以您可以很容易地为每个级别测试不同的平面颜色，并查看它们是否确实被正确获取(实际上，如果您不确定导入器，可能也值得首先在像素着色器中尝试)。
epggiuax2#
您需要将
GL_TEXTURE_MIN_FILTER设置为GL_LINEAR_MIPMAP_LINEAR或其他mipmap模式。