add grid mesh for user convenience

include/bounce/collision/shapes/grid_mesh.h

@@ -0,0 +1,92 @@
+/*
+* Copyright (c) 2016-2016 Irlan Robson http://www.irlan.net
+*
+* This software is provided 'as-is', without any express or implied
+* warranty.  In no event will the authors be held liable for any damages
+* arising from the use of this software.
+* Permission is granted to anyone to use this software for any purpose,
+* including commercial applications, and to alter it and redistribute it
+* freely, subject to the following restrictions:
+* 1. The origin of this software must not be misrepresented; you must not
+* claim that you wrote the original software. If you use this software
+* in a product, an acknowledgment in the product documentation would be
+* appreciated but is not required.
+* 2. Altered source versions must be plainly marked as such, and must not be
+* misrepresented as being the original software.
+* 3. This notice may not be removed or altered from any source distribution.
+*/
+
+#ifndef B3_GRID_MESH_H
+#define B3_GRID_MESH_H
+
+#include <bounce/collision/shapes/mesh.h>
+
+template<u32 H = 1, u32 W = 1>
+struct b3GridMesh : public b3Mesh
+{
+	b3Vec3 gridVertices[ (H + 1) * (W + 1) ];
+	b3Triangle gridTriangles[2 * H * W];
+
+	// Set this grid to a W (width) per H (height) dimensioned grid centered at the origin and aligned
+	// with the world x-z axes.
+	b3GridMesh()
+	{
+		u32 h = H + 1;
+		u32 w = W + 1;
+
+		b3Vec3 t;
+		t.x = -0.5f * float32(w) + 0.5f;
+		t.y = 0.0f;
+		t.z = -0.5f * float32(h) + 0.5f;
+
+		for (u32 i = 0; i < h; ++i)
+		{
+			for (u32 j = 0; j < w; ++j)
+			{
+				u32 v1 = i * w + j;
+
+				b3Vec3 v;
+				v.x = float32(j);
+				v.y = 0.0f;
+				v.z = float32(i);
+
+				v += t;
+
+				gridVertices[v1] = v;
+			}
+		}
+
+		u32 triangleIndex = 0;
+		for (u32 i = 0; i < h - 1; ++i)
+		{
+			for (u32 j = 0; j < w - 1; ++j)
+			{
+				u32 v1 = i * w + j;
+				u32 v2 = (i + 1) * w + j;
+				u32 v3 = (i + 1) * w + (j + 1);
+				u32 v4 = i * w + (j + 1);
+
+				b3Triangle* t1 = gridTriangles + triangleIndex;
+				++triangleIndex;
+
+				t1->v1 = v3;
+				t1->v2 = v2;
+				t1->v3 = v1;
+
+				b3Triangle* t2 = gridTriangles + triangleIndex;
+				++triangleIndex;
+
+				t2->v1 = v1;
+				t2->v2 = v4;
+				t2->v3 = v3;
+			}
+		}
+
+		vertices = gridVertices;
+		vertexCount = (H + 1) * (W + 1);
+		triangles = gridTriangles;
+		triangleCount = 2 * H * W;
+	}
+};
+
+#endif