Added btCudaBroadphase, some early research & development work to accelerate Bullet using CUDA

Re-uses the NVidia particle demo.

Extras/CUDA/shaders.cpp

@@ -0,0 +1,41 @@
+#define STRINGIFY(A) #A
+
+// vertex shader
+const char *vertexShader = STRINGIFY(
+uniform float pointRadius;  // point size in world space
+uniform float pointScale;   // scale to calculate size in pixels
+uniform float densityScale;
+uniform float densityOffset;
+void main()
+{
+    // calculate window-space point size
+    vec3 posEye = vec3(gl_ModelViewMatrix * vec4(gl_Vertex.xyz, 1.0));
+    float dist = length(posEye);
+    gl_PointSize = pointRadius * (pointScale / dist);
+
+    gl_TexCoord[0] = gl_MultiTexCoord0;
+    gl_Position = gl_ModelViewProjectionMatrix * vec4(gl_Vertex.xyz, 1.0);
+
+    gl_FrontColor = gl_Color;
+}
+);
+
+// pixel shader for rendering points as shaded spheres
+const char *spherePixelShader = STRINGIFY(
+void main()
+{
+    const vec3 lightDir = vec3(0.577, 0.577, 0.577);
+
+    // calculate normal from texture coordinates
+    vec3 N;
+    N.xy = gl_TexCoord[0].xy*vec2(2.0, -2.0) + vec2(-1.0, 1.0);
+    float mag = dot(N.xy, N.xy);
+    if (mag > 1.0) discard;   // kill pixels outside circle
+    N.z = sqrt(1.0-mag);
+
+    // calculate lighting
+    float diffuse = max(0.0, dot(lightDir, N));
+
+    gl_FragColor = gl_Color * diffuse;
+}
+);