Don't write camera aperture parameters if they're already set (Autode…

…sk#1952) * Don't author camera aperture parameters if they're already set MTOA-1951 * Add changelog * Remove spurious empty line
PrismPipeline · Jun 26, 2024 · 5e2e35c · 5e2e35c
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -14,6 +14,7 @@
 - [usd#1927](https://github.com/Autodesk/arnold-usd/issues/1927) - Fix procedural updates during iteractive changes of non-leaf primitives
 - [usd#1661](https://github.com/Autodesk/arnold-usd/issues/1661) - In the procedural the subdivision meshes will use the normals generated by the subdivision algorithm instead of the normal primvar.
 - [usd#1919](https://github.com/Autodesk/arnold-usd/issues/1919) - Fix rendering multiple frames with husk.
+- [usd#1952](https://github.com/Autodesk/arnold-usd/issues/1952) - Don't write camera aperture parameters if they're already set
 
 ## Pending bugfix release
 - [usd#1940](https://github.com/Autodesk/arnold-usd/issues/1940) - Incorrect handling of shaders referenced in multiple materials

diff --git a/libs/translator/writer/write_camera.cpp b/libs/translator/writer/write_camera.cpp
@@ -58,21 +58,28 @@ void UsdArnoldWriteCamera::Write(const AtNode *node, UsdArnoldWriter &writer)
 
     if (persp) {
         AtNode *options = AiUniverseGetOptions(writer.GetUniverse());
-
-        float fov = AiNodeGetFlt(node, AtString("fov"));
-        float horizontalAperature = tan(fov * AI_DTOR * 0.5f);
-        horizontalAperature *= (2.f * 50.f * GfCamera::FOCAL_LENGTH_UNIT);
-        horizontalAperature /= GfCamera::APERTURE_UNIT;
-
-        writer.SetAttribute(cam.CreateHorizontalApertureAttr(), horizontalAperature);
-        float verticalAperture = horizontalAperature;
-
-        // Use the options image resolution to determine the vertical aperture
-        if (options) {
-            verticalAperture *= (float)AiNodeGetInt(options, AtString("yres")) / (float)AiNodeGetInt(options, AtString("xres"));
+        // Arnold only knows about FOV and not about horizontal & vertical aperture.
+        // We want to dump some aperture values in the usd file, as this is used by other
+        // usd tools, but we can't compute an exact value (we'd need a focal length)
+        // we only author these values if they weren't previously set. MTOA-1951
+        if (!cam.GetHorizontalApertureAttr().HasAuthoredValue() && 
+                !cam.GetVerticalApertureAttr().HasAuthoredValue()) {
+
+            float fov = AiNodeGetFlt(node, AtString("fov"));
+            float horizontalAperature = tan(fov * AI_DTOR * 0.5f);
+            // The formula below assumes a focal length of 50, which is the default value but 
+            // not necessarily the right one. Therefore we can't author an exact value here.
+            horizontalAperature *= (2.f * 50.f * GfCamera::FOCAL_LENGTH_UNIT);
+            horizontalAperature /= GfCamera::APERTURE_UNIT;
+            writer.SetAttribute(cam.CreateHorizontalApertureAttr(), horizontalAperature);
+
+            float verticalAperture = horizontalAperature;
+            // Use the options image resolution to determine the vertical aperture
+            if (options) {
+                verticalAperture *= (float)AiNodeGetInt(options, AtString("yres")) / (float)AiNodeGetInt(options, AtString("xres"));
+            }
+            writer.SetAttribute(cam.CreateVerticalApertureAttr(), verticalAperture);
         }
-
-        writer.SetAttribute(cam.CreateVerticalApertureAttr(), verticalAperture);
         // Note that we're not adding "fov" to the list of exported attrs, because we still
         // want it to be set as an arnold-specific attribute. This way, when it's read from usd,
         // we can get the exact same value without any difference caused by the back and forth conversions