Fix CSGSphere3D mesh creation

1 files changed, 35 insertions, 31 deletions

diff --git a/modules/csg/csg_shape.cpp b/modules/csg/csg_shape.cpp
index 73c1ba554c..b47fa35f1a 100644
--- a/modules/csg/csg_shape.cpp
+++ b/modules/csg/csg_shape.cpp
@@ -923,36 +923,40 @@ CSGBrush *CSGSphere3D::_build_brush() {
 		Ref<Material> *materialsw = materials.ptrw();
 		bool *invertw = invert.ptrw();
 
-		const double lat_step = 1.0 / rings;
-		const double lon_step = 1.0 / radial_segments;
+		// We want to follow an order that's convenient for UVs.
+		// For latitude step we start at the top and move down like in an image.
+		const double latitude_step = -Math_PI / rings;
+		const double longitude_step = Math_TAU / radial_segments;
 		int face = 0;
-		for (int i = 1; i <= rings; i++) {
-			double lat0 = Math_PI * (0.5 - (i - 1) * lat_step);
-			double c0 = Math::cos(lat0);
-			double s0 = Math::sin(lat0);
-			double v0 = double(i - 1) / rings;
-
-			double lat1 = Math_PI * (0.5 - i * lat_step);
-			double c1 = Math::cos(lat1);
-			double s1 = Math::sin(lat1);
-			double v1 = double(i) / rings;
-
-			for (int j = 1; j <= radial_segments; j++) {
-				double lng0 = Math_TAU * (0.5 - (j - 1) * lon_step);
-				double x0 = Math::cos(lng0);
-				double y0 = Math::sin(lng0);
-				double u0 = double(j - 1) / radial_segments;
-
-				double lng1 = Math_TAU * (0.5 - j * lon_step);
-				double x1 = Math::cos(lng1);
-				double y1 = Math::sin(lng1);
-				double u1 = double(j) / radial_segments;
+		for (int i = 0; i < rings; i++) {
+			double latitude0 = latitude_step * i + Math_TAU / 4;
+			double cos0 = Math::cos(latitude0);
+			double sin0 = Math::sin(latitude0);
+			double v0 = double(i) / rings;
+
+			double latitude1 = latitude_step * (i + 1) + Math_TAU / 4;
+			double cos1 = Math::cos(latitude1);
+			double sin1 = Math::sin(latitude1);
+			double v1 = double(i + 1) / rings;
+
+			for (int j = 0; j < radial_segments; j++) {
+				double longitude0 = longitude_step * j;
+				// We give sin to X and cos to Z on purpose.
+				// This allows UVs to be CCW on +X so it maps to images well.
+				double x0 = Math::sin(longitude0);
+				double z0 = Math::cos(longitude0);
+				double u0 = double(j) / radial_segments;
+
+				double longitude1 = longitude_step * (j + 1);
+				double x1 = Math::sin(longitude1);
+				double z1 = Math::cos(longitude1);
+				double u1 = double(j + 1) / radial_segments;
 
 				Vector3 v[4] = {
-					Vector3(x0 * c0, s0, y0 * c0) * radius,
-					Vector3(x1 * c0, s0, y1 * c0) * radius,
-					Vector3(x1 * c1, s1, y1 * c1) * radius,
-					Vector3(x0 * c1, s1, y0 * c1) * radius,
+					Vector3(x0 * cos0, sin0, z0 * cos0) * radius,
+					Vector3(x1 * cos0, sin0, z1 * cos0) * radius,
+					Vector3(x1 * cos1, sin1, z1 * cos1) * radius,
+					Vector3(x0 * cos1, sin1, z0 * cos1) * radius,
 				};
 
 				Vector2 u[4] = {
@@ -962,8 +966,8 @@ CSGBrush *CSGSphere3D::_build_brush() {
 					Vector2(u0, v1),
 				};
 
-				if (i < rings) {
-					//face 1
+				// Draw the first face, but skip this at the north pole (i == 0).
+				if (i > 0) {
 					facesw[face * 3 + 0] = v[0];
 					facesw[face * 3 + 1] = v[1];
 					facesw[face * 3 + 2] = v[2];
@@ -979,8 +983,8 @@ CSGBrush *CSGSphere3D::_build_brush() {
 					face++;
 				}
 
-				if (i > 1) {
-					//face 2
+				// Draw the second face, but skip this at the south pole (i == rings - 1).
+				if (i < rings - 1) {
 					facesw[face * 3 + 0] = v[2];
 					facesw[face * 3 + 1] = v[3];
 					facesw[face * 3 + 2] = v[0];