make the IES octahedral maps corner sampled

Author: devsh

examples_tests

@@ -6,25 +6,33 @@
 
 #include <nbl/builtin/glsl/math/constants.glsl>
 
-// TODO: implement proper mirroing
-// MIRROR_180_BITS = 0b001, Last Angle is 180, so map V slightly differently
-// MIRROR_90_BITS = 0b010, Last Angle is 90, so map both U and V slightly differently
-// ISOTROPIC_BITS = 0b011, texture to sample is Nx1, pretend v=middle always  
-// FULL_THETA_BIT = 0b100, handle extended domain and rotate by 45 degrees for anisotropic
-
-vec2 nbl_glsl_IES_convert_dir_to_uv(vec3 dir) {
-    float sum = dot(vec3(1.0f), abs(dir));        
+// TODO: when rewriting to HLSL this is not IES namespace or folder, this should be octahedral mapping sitting somewhere where the spherical/polar sits
+// NOTE: I changed it to return NDC [-1,1]^2 instead of UV coords [0,1]^2
+vec2 nbl_glsl_TODOnamespace_octahedral_mapping(vec3 dir)
+{
+    float sum = dot(vec3(1.0f), abs(dir));
     vec3 s = dir / sum;    
 
-    if(s.z < 0.0f) {
-        s.xy = sign(s.xy) * (1.0f - abs(s.yx));
+    if(s.z < 0.0f)
+    {
+        const uvec2 flipSignMask = floatBitsToUint(s.xy)&0x80000000u;
+        s.xy = uintBitsToFloat(floatBitsToUint(1.0f - abs(s.yx))^flipSignMask);
     }
 
-    return s.xy * 0.5f + 0.5f;
+    return s.xy;
 }
 
-// vec2 nbl_glsl_IES_convert_dir_to_uv(vec3 dir) {
-// 	return vec2((atan(dir.x, dir.y) + nbl_glsl_PI) / (2.0*nbl_glsl_PI), acos(dir.z) / nbl_glsl_PI);
-// }
+// TODO: implement proper mirroing
+// MIRROR_180_BITS = 0b001, Last Angle is 180, so map V with MIRROR and corner sampling off
+// MIRROR_90_BITS = 0b010, Last Angle is 90, so map both U and V with MIRROR and corner sampling off
+// ISOTROPIC_BITS = 0b011, texture to sample is Nx1, pretend v=middle always , and make u REPEAT or CLAMP_TO_BORDER
+// FULL_THETA_BIT = 0b100, handle truncated domain and rotate by 45 degrees for anisotropic
+// (certain combos wont work like 90 degree 2 symmetry domain & half theta), it really needs to be an 8 case label thing explicitly enumerated
+vec2 nbl_glsl_IES_convert_dir_to_uv(vec3 dir, vec2 halfMinusHalfPixel)
+{
+    // halfMinusHalfPixel = 0.5-0.5/texSize
+    // believe it or not, cornerSampled(NDC*0.5+0.5) = NDC*0.5*(1-1/texSize)+0.5
+    return nbl_glsl_TODOnamespace_octahedral_mapping(dir)*halfMinusHalfPixel+0.5;
+}
 
 #endif

include/nbl/builtin/glsl/ies/functions.glsl

@@ -601,7 +601,8 @@ vec3 nbl_glsl_MC_oriented_material_t_getEmissive(in nbl_glsl_MC_oriented_materia
 		if ((floatBitsToInt(emitter.orientation[0])&1u) != 1u) {
 			right *= -1;
 		}
-		return emissive * nbl_glsl_vTextureGrad(emitter.emissionProfile, nbl_glsl_IES_convert_dir_to_uv(mat3(right, up, view)*dir), mat2(0.0)).r;
+		vec2 halfMinusHalfPixel = 0.5-0.5/vec2(nbl_glsl_unpackSize(emitter.emissionProfile));
+		return emissive * nbl_glsl_vTextureGrad(emitter.emissionProfile, nbl_glsl_IES_convert_dir_to_uv(mat3(right, up, view)*dir,halfMinusHalfPixel), mat2(0.0)).r;
 	}
 #endif
 	return emissive;

include/nbl/builtin/glsl/material_compiler/common.glsl

@@ -88,8 +88,8 @@ inline core::vectorSIMDf CIESProfile::octahdronUVToDir(const float& u, const flo
     float abs_x = core::abs(pos.x), abs_y = core::abs(pos.y);
     pos.z = 1.0 - abs_x - abs_y;
     if (pos.z < 0.0) {
-        pos.x = core::sign(pos.x) * (1.0 - abs_y);
-        pos.y = core::sign(pos.y) * (1.0 - abs_x);
+        pos.x = (pos.x<0.f ? (-1.f):1.f) * (1.0 - abs_y);
+        pos.y = (pos.y<0.f ? (-1.f):1.f) * (1.0 - abs_x);
     }
 
     return core::normalize(pos);
@@ -116,6 +116,8 @@ core::smart_refctd_ptr<asset::ICPUImageView> CIESProfile::createIESTexture(Execu
     if (height > CDC_MAX_TEXTURE_HEIGHT)
         height = CDC_MAX_TEXTURE_HEIGHT;
 
+    // TODO: If no symmetry (no folding in half and abuse of mirror sampler) make dimensions odd-sized so middle texel taps the south pole
+
     asset::ICPUImage::SCreationParams imgInfo;
     imgInfo.type = asset::ICPUImage::ET_2D;
     imgInfo.extent.width = width;
@@ -161,15 +163,19 @@ core::smart_refctd_ptr<asset::ICPUImageView> CIESProfile::createIESTexture(Execu
         const double maxValue = getMaxCandelaValue();
         const double maxValueRecip = 1.0 / maxValue;
 
-        const double vertInv = 1.0 / height;
-        const double horiInv = 1.0 / width;
+        // There is one huge issue, the IES files love to give us values for degrees 0, 90, 180 an 360
+        // So standard octahedral mapping won't work, because for above data points you need corner sampled images.
+        const float vertInv = 1.0 / (height-1);
+        const float horiInv = 1.0 / (width-1);
 
         const double flattenTarget = getAvgEmmision(fullDomainFlatten);
         const double domainLo = core::radians(vAngles.front());
         const double domainHi = core::radians(vAngles.back());
         auto fill = [&](uint32_t blockArrayOffset, core::vectorSIMDu32 position) -> void
         {
-            const auto dir = octahdronUVToDir(((float)position.x + 0.5) * vertInv, ((float)position.y + 0.5) * horiInv);
+            // We don't currently support generating IES images that exploit symmetries or reduced domains, all are full octahederal mappings of a sphere.
+            // If we did, we'd rely on MIRROR and CLAMP samplers to do some of the work for us while handling the discontinuity due to corner sampling. 
+            const auto dir = octahdronUVToDir(position.x * vertInv, position.y * horiInv);
             const auto [theta, phi] = sphericalDirToRadians(dir);
             const auto intensity = sample(theta, phi);