From 69f538e1de1670c9441eeb9f7a8f15e1646327bc Mon Sep 17 00:00:00 2001
From: Qianyue He <984041003@qq.com>
Date: Tue, 23 Apr 2024 23:20:25 +0800
Subject: [PATCH] Bug fix: sphere emitter cosine hemisphere sampling measure
 conversion.

---
 emitters/abtract_source.py     | 19 +++++++++++++------
 scenes/csphere/balls-multi.xml | 12 ++++++------
 scenes/csphere/single-ball.xml |  2 +-
 3 files changed, 20 insertions(+), 13 deletions(-)

diff --git a/emitters/abtract_source.py b/emitters/abtract_source.py
index ea7f972..761dda0 100644
--- a/emitters/abtract_source.py
+++ b/emitters/abtract_source.py
@@ -22,6 +22,8 @@
 from rich.console import Console
 CONSOLE = Console(width = 128)
 
+HEMISPHERE_SAMPLE_SPHERE = True
+
 # point-0: PointSource, area-1: AreaSource, spot-2: SpotSource, collimated-4: CollimatedSource
 
 # =============== Emitter Type =================
@@ -102,13 +104,18 @@ def sample_hit(
                 tri_id    = prim_info[self.obj_ref_id, 0]
                 center    = dvs[tri_id, 0]
                 radius    = dvs[tri_id, 1][0]
-                to_hit    = (hit_pos - center).normalized()
-                # the pdf here can be viewed as being both both sa & area measure
-                # since for a unit sphere, different unit solid angle extends to the same amount of area
-                local_dir, pdf = cosine_hemisphere()
-                normal, _ = delocalize_rotate(to_hit, local_dir)
+                
+                if ti.static(HEMISPHERE_SAMPLE_SPHERE):
+                    to_hit    = (hit_pos - center).normalized()
+                    # the pdf here can be viewed as being both both sa & area measure
+                    # since for a unit sphere, different unit solid angle extends to the same amount of area
+                    local_dir, pdf = uniform_sphere()
+                    normal, _ = delocalize_rotate(to_hit, local_dir)
+                    ret_pos   = center + normal * radius
+                    ret_pdf   = pdf / (radius * radius)
+                else:
+                    normal, _pdf = uniform_sphere()
                 ret_pos   = center + normal * radius
-                ret_pdf   = pdf
             else:
                 mesh_num = prim_info[self.obj_ref_id, 1]
                 tri_id    = (ti.random(int) % mesh_num) + prim_info[self.obj_ref_id, 0]  # ASSUME that triangles are similar in terms of area
diff --git a/scenes/csphere/balls-multi.xml b/scenes/csphere/balls-multi.xml
index eb332ac..aae04ab 100644
--- a/scenes/csphere/balls-multi.xml
+++ b/scenes/csphere/balls-multi.xml
@@ -88,21 +88,21 @@
 		</medium>
 	</bsdf>
 
-	<emitter type="area" id="area">
+	<!-- <emitter type="area" id="area">
 		<rgb name="emission" value="70.0, 63.2, 60.3"/>
 		<rgb name="scaler" value="0.15"/>
-	</emitter>
+	</emitter> -->
 
 	<emitter type="area" id="ball_emit">
 		<rgb name="emission" value="2.0, 1.5, 1.3"/>
-		<rgb name="scaler" value="0.15"/>
+		<rgb name="scaler" value="2"/>
 	</emitter>
 
-	<emitter type="point" id="point">
+	<!-- <emitter type="point" id="point">
 		<rgb name="emission" value="60.0, 60., 60.0"/>
 		<rgb name="scaler" value="0.15"/>
 		<point name="center" x="2.779" y="3.0" z="-1.0"/>
-	</emitter>
+	</emitter> -->
 
 	<shape type="obj">
 		<string name="filename" value="../meshes/cornell/cbox_luminaire.obj"/>
@@ -110,7 +110,7 @@
 			<translate x="0" y="-0.001" z="0"/>
 		</transform>
 		<ref type="material" id="light"/>
-		<ref type="emitter" id="area"/>
+		<!-- <ref type="emitter" id="area"/> -->
 	</shape>
 
 	<shape type="obj">
diff --git a/scenes/csphere/single-ball.xml b/scenes/csphere/single-ball.xml
index 20b5da8..c6dc50b 100644
--- a/scenes/csphere/single-ball.xml
+++ b/scenes/csphere/single-ball.xml
@@ -10,7 +10,7 @@
 		<float name="fov" value="39.3077"/>
         <integer name="sample_count" value="128"/>
         <integer name="max_bounce" value="12"/>
-        <integer name="num_shadow_ray" value="0"/>       
+        <integer name="num_shadow_ray" value="1"/>       
 
 		<integer name="start_t" value="1"/>       
         <integer name="end_t" value="100"/>