Fix image probe FOV calculation

Fix FOV equations. Also, fix case for FOV of 180 degrees where image
lighting map was used in wrong orientation. With this fix, the negative z
axis passes through the center of the lighting map, with edges of the image
wrapped around the scene, i.e. with default camera settings the center of
image is in the direction of camera. This holds true for both cases of FOV = 180 and
FOV < 180 degrees.

This fix must be replicated on editor side for results to match.

Task-ID: QT3DS-154

Change-Id: Idb8071dcd74cc3d5b17c964239bec9a52b4fe6b8
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

1 files changed, 9 insertions, 3 deletions

diff --git a/res/effectlib/sampleProbe.glsllib b/res/effectlib/sampleProbe.glsllib
index 43024ec..fc40541 100644
--- a/res/effectlib/sampleProbe.glsllib
+++ b/res/effectlib/sampleProbe.glsllib
@@ -97,10 +97,16 @@ vec2 getProbeSampleUV( vec3 smpDir, vec4 probeRot, vec2 probeOfs )
     vec2 smpUV;
 
 #if QT3DS_ENABLE_IBL_FOV
-    smpUV.x = (2.0 * atan(-smpDir.z, smpDir.x) + 3.14159265358 ) / light_probe_opts.x;
-    smpUV.y = (2.0 * atan(-smpDir.z, smpDir.y) + 3.14159265358 ) / light_probe_opts.x;
+    smpUV = vec2(atan(smpDir.x, smpDir.z), asin(smpDir.y));
+    // assume equirectangular HDR spherical map (instead of cube map) and map sample
+    // UV coordinates accordingly
+    smpUV *= 2.0 * vec2(0.1591596371160, 0.318319274232054);
+    // Default FOV is 180 deg = pi rad. Narrow the FOV
+    // by scaling texture coordinates by the ratio of
+    // incoming FOV to 180 degrees default
+    smpUV *= 3.14159265358 / light_probe_opts.x;
 #else
-    smpUV.x = atan( smpDir.x, -smpDir.z) / 3.14159265359;
+    smpUV.x = atan( smpDir.x, smpDir.z) / 3.14159265359;
     smpUV.y = 1.0 - (acos(smpDir.y) / 1.57079632679);
 #endif
     smpUV = transformSample( smpUV.xy * 0.5, probeRot, probeOfs ) + vec2(0.5, 0.5);