Lib Sparse - Shader API
lib-sparse.glsl
This file provides useful functions to ensure sparse textures sampling correctness (ARB_sparse_texture). Allows to sample only part of textures really present in video memory.
Public Functions: getSparseCoord getSparseCoordLod0 textureSparseQueryLod textureSparse
Public Structures: SamplerSparse SparseCoord
The FEATURE_SPARSE_TEXTURE macro is defined only if the sparse virtual texture extension is enabled.
If enabled, process additional texture lookup checks to climb up mipmap pyramid if texels are missing.
## ifdef FEATURE_SPARSE_TEXTURE
//: param auto material_lod_check_needed
uniform bool material_lod_check_needed = false;
//: param auto material_lod_mask
uniform usampler2D material_lod_mask;
## endif // FEATURE_SPARSE_TEXTURE
//: param auto uvtile_reference_sampler
uniform sampler2D uvtile_reference_sampler;
//: param auto uvtile_size
uniform vec2 uvtile_size;
//: param auto uvtile_inverse_size
uniform vec2 uvtile_inverse_size;
//: param auto uvtile_lod_bias
uniform float uvtile_lod_bias;
Sampler and sparse texture information structure
Used to query all sampler related uniforms with a single auto binding
struct SamplerSparse {
sampler2D tex;
vec4 size; // width, height, 1/width, 1/height
bool is_set; // a boolean indicating whether the texture is in the texture set or not
uvec3 lod_mask_select; // masking operations description allowing to retrieve loaded mipmaps information
};
Sparse sampling coordinates
Store the UV coordinates & material-wise sparse LoD mask
struct SparseCoord {
vec2 tex_coord;
vec2 dfdx;
vec2 dfdy;
float lod;
uint material_lod_mask;
};
## if defined(SHADER_FRAGMENT)
Build texture coordinates structure used by textureSparse() sampling function (must be called from fragment shader)
Example: SparseCoord uv1coord = getSparseCoord(inputs.multi_tex_coord[1]);
SparseCoord getSparseCoord(vec2 tex_coord) {
SparseCoord res;
res.tex_coord = tex_coord;
res.dfdx = dFdx(tex_coord);
res.dfdy = dFdy(tex_coord);
## ifdef FEATURE_SPARSE_TEXTURE
res.material_lod_mask = material_lod_check_needed ?
textureLod(material_lod_mask,tex_coord,0.0).r :
0u;
res.lod = getLodFromReferenceSampler(tex_coord);
## endif // FEATURE_SPARSE_TEXTURE
return res;
}
## endif
Build texture coordinates structure used by textureSparse() sampling function Base level sampling version (can be used if outside fragment shader)
SparseCoord getSparseCoordLod0(vec2 tex_coord) {
SparseCoord res;
res.tex_coord = tex_coord;
res.dfdx = vec2(0.0);
res.dfdy = vec2(0.0);
## ifdef FEATURE_SPARSE_TEXTURE
res.material_lod_mask = material_lod_check_needed ?
textureLod(material_lod_mask,tex_coord,0.0).r :
0u;
res.lod = 0.0;
## endif // FEATURE_SPARSE_TEXTURE
return res;
}
## if defined(SHADER_FRAGMENT)
Compute the level-of-detail that would be used to sample from a sparse texture
Climb up mipmap pyramid if texels are missing Returns LoD BEFORE LoD bias applied
float textureSparseQueryLod(SamplerSparse sampler, SparseCoord coord) {
## ifdef FEATURE_SPARSE_TEXTURE
float lodfix = coord.lod;
if (material_lod_check_needed) {
lodfix = getFixedSparseLod(getTextureLodMask(sampler.lod_mask_select, coord.material_lod_mask), lodfix);
}
return lodfix-uvtile_lod_bias;
## else // FEATURE_SPARSE_TEXTURE
return textureQueryLod(sampler.tex, coord.tex_coord).y-uvtile_lod_bias;
## endif // FEATURE_SPARSE_TEXTURE
}
## endif // SHADER_FRAGMENT
Compute the derivatives that would be used to sample from a sparse texture
Climb up mipmap pyramid if texels are missing
void textureSparseQueryGrad(out vec2 dfdx, out vec2 dfdy, SamplerSparse sampler, SparseCoord coord) {
## ifdef FEATURE_SPARSE_TEXTURE
if (material_lod_check_needed) {
float lodfix = getFixedSparseLod(getTextureLodMask(sampler.lod_mask_select, coord.material_lod_mask), coord.lod);
if (coord.lod!=lodfix) {
// Fix dfdx dfdy, take account offset, no more anisotropy
vec2 ddfix = exp2(lodfix-uvtile_lod_bias) * uvtile_inverse_size;
dfdx = vec2(ddfix.x,0.0);
dfdy = vec2(0.0,ddfix.y);
return;
}
}
## endif // FEATURE_SPARSE_TEXTURE
dfdx = coord.dfdx;
dfdy = coord.dfdy;
}
Performs a texture lookup on a sparse texture, go up the mipmap levels if necessary
This function replaces the standard texture(sampler2D, vec2) to retrieve texels from a sparse texture
vec4 textureSparse(SamplerSparse sampler, SparseCoord coord) {
vec2 dfdx,dfdy;
textureSparseQueryGrad(dfdx, dfdy, sampler, coord);
return textureGrad(sampler.tex, coord.tex_coord, dfdx, dfdy);
}
Given a texture, performs an optimized multiple texture lookups with small offsets
We are providing alternatives versions of this helper for up to N=4
void textureSparseOffsets(SamplerSparse sampler, SparseCoord coord, vec2 offsets[N], out vec4 results[N]) {
vec2 dfdx,dfdy;
textureSparseQueryGrad(dfdx, dfdy, sampler, coord);
for(int i = 0; i < N; ++i) {
results[i] = textureGrad(sampler.tex, coord.tex_coord + offsets[i], dfdx, dfdy);
}
}