medfall

commit 5abf4bb24e9a1d81ba9853a0c7d8a34fe8df23bf
parent 281705c3846ecc0142613c6b12960c96731be930
Author: Michael Savage <mikejsavage@gmail.com>
Date:   Sun May  8 22:04:27 +0100

Optimise immediate_sphere

Diffstat:
immediate.cc
 | 
53
++++++++++++++++++++++++++++++++++++-----------------
1 file changed, 36 insertions(+), 17 deletions(-)
diff --git a/immediate.cc b/immediate.cc
@@ -45,41 +45,60 @@ void immediate_sphere(
 	const float azimuth_max = 2.0f * M_PI;
 	const float pitch_max = M_PI;
 
+	const float dsa = sinf( 0.5f * azimuth_max / ( subdivisions - 1 ) );
+	const float dca = cosf( 0.5f * azimuth_max / ( subdivisions - 1 ) );
+	const float dsp = sinf( pitch_max / subdivisions );
+	const float dcp = cosf( pitch_max / subdivisions );
+
+	float sa0 = 0;
+	float sa1 = dsa;
+	float ca0 = 0;
+	float ca1 = dca;
+
 	for( u32 a = 0; a < subdivisions * 2; a++ ) {
-		float azimuth0 = azimuth_max * ( float ) a / ( subdivisions * 2 );
-		float azimuth1 = azimuth_max * ( float ) ( a + 1 ) / ( subdivisions * 2 );
+		float sp0 = 0;
+		float sp1 = dsp;
+		float cp0 = 0;
+		float cp1 = dcp;
 
 		for( u32 p = 0; p < subdivisions; p++ ) {
-			float pitch0 = pitch_max * ( float ) p / subdivisions;
-			float pitch1 = pitch_max * ( float ) ( p + 1 ) / subdivisions;
-
 			glm::vec3 top_left = centre + glm::vec3(
-				radius * cosf( azimuth0 ) * sinf( pitch0 ),
-				radius * sinf( azimuth0 ) * sinf( pitch0 ),
-				radius * cosf( pitch0 )
+				radius * ca0 * sp0,
+				radius * sa0 * sp0,
+				radius * cp0
 			);
 
 			glm::vec3 top_right = centre + glm::vec3(
-				radius * cosf( azimuth1 ) * sinf( pitch0 ),
-				radius * sinf( azimuth1 ) * sinf( pitch0 ),
-				radius * cosf( pitch0 )
+				radius * ca1 * sp0,
+				radius * sa1 * sp0,
+				radius * cp0
 			);
 
 			glm::vec3 bottom_left = centre + glm::vec3(
-				radius * cosf( azimuth0 ) * sinf( pitch1 ),
-				radius * sinf( azimuth0 ) * sinf( pitch1 ),
-				radius * cosf( pitch1 )
+				radius * ca0 * sp1,
+				radius * sa0 * sp1,
+				radius * cp1
 			);
 
 			glm::vec3 bottom_right = centre + glm::vec3(
-				radius * cosf( azimuth1 ) * sinf( pitch1 ),
-				radius * sinf( azimuth1 ) * sinf( pitch1 ),
-				radius * cosf( pitch1 )
+				radius * ca1 * sp1,
+				radius * sa1 * sp1,
+				radius * cp1
 			);
 
 			immediate_triangle( ctx, top_left, top_right, bottom_left, colour );
 			immediate_triangle( ctx, bottom_left, top_right, bottom_right, colour );
+
+			sp0 = sp1;
+			cp0 = cp1;
+			sp1 = sp0 * dcp + cp0 * dsp;
+			cp1 = cp0 * dcp - sp0 * dsp;
 		}
+
+		sa0 = sa1;
+		ca0 = ca1;
+		sa1 = sa0 * dca + ca0 * dsa;
+		ca1 = ca0 * dca - sa0 * dsa;
 	}
 }