lundi 13 décembre 2010

API independent primitive topology

Here is a simple uber function for retrieving the primitive topology in a native API format from an API independent format:

enum PrimitiveTopology
{
 PT_POINTS = 0,
 PT_LINES,
 PT_LINE_STRIP,
 PT_TRIANGLES,
 PT_TRIANGLE_STRIP,
 PT_TRIANGLE_FAN,
 PT_QUADS,
 PT_QUAD_STRIP
};

enum GraphicsAPI
{
 DirectX11,
 DirectX10,
 DirectX10_1,
 DirectX9,
 OpenGL,
 OpenGLES
};

template <GraphicsAPI API>
int getPrimitiveTopology(PrimitiveTopology pt)
{
 switch (API)
 {
  case DirectX11:
  case DirectX10:
  case DirectX10_1:
   switch(pt)
   {
    case PT_POINTS:
     return D3D_PRIMITIVE_TOPOLOGY_POINTLIST;
     break;
     
    case PT_LINES:
     return D3D_PRIMITIVE_TOPOLOGY_LINELIST;
     break;
     
    case PT_LINE_STRIP:
     return D3D_PRIMITIVE_TOPOLOGY_LINESTRIP;
     break;
     
    case PT_TRIANGLES:
     return D3D_PRIMITIVE_TOPOLOGY_TRIANGLELIST;
     break;
     
    case PT_TRIANGLE_STRIP:
     return D3D_PRIMITIVE_TOPOLOGY_TRIANGLESTRIP;
     break;
     
    case PT_TRIANGLE_FAN:
     return D3D_PRIMITIVE_TOPOLOGY_UNDEFINED;
     break;
     
    default:
     assert(0 && "getPrimitiveTopology::DirectX10+ Unknown or unsupported primitive topology !");
     return -1;
     break;
   }
   break;
  case DirectX9:
   switch(pt)
   {
    case PT_POINTS:
     return D3DPT_POINTLIST;
     break;
     
    case PT_LINES:
     return D3DPT_LINELIST;
     break;
     
    case PT_LINE_STRIP:
     return D3DPT_LINESTRIP;
     break;
     
    case PT_TRIANGLES:
     return D3DPT_TRIANGLELIST;
     break;
     
    case PT_TRIANGLE_STRIP:
     return D3DPT_TRIANGLESTRIP;
     break;
     
    case PT_TRIANGLE_FAN:
     return D3DPT_TRIANGLEFAN;
     break;
     
    default:
     assert(0 && "getPrimitiveTopology::DirectX9 Unknown or unsupported primitive topology !");
     return -1;
     break;
   }
   break;
  case OpenGL:
  case OpenGLES:
   switch(pt)
   {
    case PT_POINTS:
     return GL_POINTS;
     break;
     
    case PT_LINES:
     return GL_LINES;
     break;
     
    case PT_LINE_STRIP:
     return GL_LINE_STRIP;
     break;
     
    case PT_TRIANGLES:
     return GL_TRIANGLES;
     break;
     
    case PT_TRIANGLE_STRIP:
     return GL_TRIANGLE_STRIP;
     break;
     
    case PT_TRIANGLE_FAN:
     return GL_TRIANGLE_FAN;
     break;
    default:
     assert(0 && "getPrimitiveTopology::OpenGL/ES Unknown or unsupported primitive topology !");
     return -1;
     break;
   }
   break;
  default:
   assert(0 && "getPrimitiveTopology() Unknown API !");
   return -1;
   break;
 }
}


A good compiler should optimize the dead code.
Also if you want to avoid the dependency on the graphics API headers, here are the necessary enums:


enum D3D_PRIMITIVE_TOPOLOGY
{
 D3D_PRIMITIVE_TOPOLOGY_UNDEFINED = 0,
 D3D_PRIMITIVE_TOPOLOGY_POINTLIST = 1,
 D3D_PRIMITIVE_TOPOLOGY_LINELIST = 2,
 D3D_PRIMITIVE_TOPOLOGY_LINESTRIP = 3,
 D3D_PRIMITIVE_TOPOLOGY_TRIANGLELIST = 4,
 D3D_PRIMITIVE_TOPOLOGY_TRIANGLESTRIP = 5
};

enum D3DPRIMITIVETYPE
{
 D3DPT_POINTLIST = 1,
 D3DPT_LINELIST = 2,
 D3DPT_LINESTRIP = 3,
 D3DPT_TRIANGLELIST = 4,
 D3DPT_TRIANGLESTRIP = 5,
 D3DPT_TRIANGLEFAN = 6,
 D3DPT_FORCE_DWORD = 0x7fffffff,
};

enum GLPrimitiveTopology
{
 GL_POINTS                        = 0x0000,
 GL_LINES                         = 0x0001,
 GL_LINE_LOOP                     = 0x0002,
 GL_LINE_STRIP                    = 0x0003,
 GL_TRIANGLES                     = 0x0004,
 GL_TRIANGLE_STRIP                = 0x0005,
 GL_TRIANGLE_FAN                  = 0x0006,
 GL_QUADS                         = 0x0007,
 GL_QUAD_STRIP                    = 0x0008,
 GL_POLYGON                       = 0x0009,
};

If you define the native types yourself, watch out for conflicts !

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