Use vertical instead of horizontal FOV in HMM_Perspective (HandmadeMa…

…th#101) * Use vertical instead of horizontal FOV * Update readme * Fix tests
GsxCasper · Jul 10, 2019 · 93e56be · 93e56be
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commit 93e56be
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Showing 3 changed files with 10 additions and 7 deletions.
diff --git a/HandmadeMath.h b/HandmadeMath.h
@@ -1186,10 +1186,12 @@ HMM_INLINE hmm_mat4 HMM_Perspective(float FOV, float AspectRatio, float Near, fl
 {
     hmm_mat4 Result = HMM_Mat4();
 
-    float TanThetaOver2 = HMM_TanF(FOV * (HMM_PI32 / 360.0f));
+    // See https://www.khronos.org/registry/OpenGL-Refpages/gl2.1/xhtml/gluPerspective.xml
+
+    float Cotangent = 1.0f / HMM_TanF(FOV * (HMM_PI32 / 360.0f));
 
-    Result.Elements[0][0] = 1.0f / TanThetaOver2;
-    Result.Elements[1][1] = AspectRatio / TanThetaOver2;
+    Result.Elements[0][0] = Cotangent / AspectRatio;
+    Result.Elements[1][1] = Cotangent;
     Result.Elements[2][3] = -1.0f;
     Result.Elements[2][2] = (Near + Far) / (Near - Far);
     Result.Elements[3][2] = (2.0f * Near * Far) / (Near - Far);

diff --git a/README.md b/README.md
@@ -10,6 +10,7 @@ To get started, go download [the latest release](https://github.com/HandmadeMath
 
 Version         | Changes        |
 ----------------|----------------|
+**1.10.0** | Made HMM_Perspective use vertical FOV instead of horizontal FOV for consistency with other graphics APIs. |
 **1.9.0** | Added SSE versions of quaternion operations. |
 **1.8.0** | Added fast vector normalization routines that use fast inverse square roots.
 **1.7.1** | Changed operator[] to take a const ref int instead of an int.

diff --git a/test/categories/Projection.h b/test/categories/Projection.h
@@ -20,16 +20,16 @@ TEST(Projection, Perspective)
     {
         hmm_vec3 original = HMM_Vec3(5.0f, 5.0f, -15.0f);
         hmm_vec4 projected = HMM_MultiplyMat4ByVec4(projection, HMM_Vec4v(original, 1));
-        EXPECT_FLOAT_EQ(projected.X, 5.0f);
-        EXPECT_FLOAT_EQ(projected.Y, 10.0f);
+        EXPECT_FLOAT_EQ(projected.X, 2.5f);
+        EXPECT_FLOAT_EQ(projected.Y, 5.0f);
         EXPECT_FLOAT_EQ(projected.Z, 15.0f);
         EXPECT_FLOAT_EQ(projected.W, 15.0f);
     }
     {
         hmm_vec3 original = HMM_Vec3(5.0f, 5.0f, -5.0f);
         hmm_vec4 projected = HMM_MultiplyMat4ByVec4(projection, HMM_Vec4v(original, 1));
-        EXPECT_FLOAT_EQ(projected.X, 5.0f);
-        EXPECT_FLOAT_EQ(projected.Y, 10.0f);
+        EXPECT_FLOAT_EQ(projected.X, 2.5f);
+        EXPECT_FLOAT_EQ(projected.Y, 5.0f);
         EXPECT_FLOAT_EQ(projected.Z, -5.0f);
         EXPECT_FLOAT_EQ(projected.W, 5.0f);
     }