Thread: DX surfaces or textures?

Hi all,

Here's my situation:

I have a bitmap (background... map of europe) that's 1152 x 965. As such, some of the countries and bodies of water are greater that 256 x 256 in size.

I'm trying to figure out a way to make a "highlighter" for when a user clicks on one country and scrolls over another. The country clicked on should change color, and the country moused over to should also change color.

I need the background to still be visible underneath this, due to having text on it.

I was thinking of using textures to accomplish this, by creating a bunch of bitmaps for the countries (which would be the highlight color), but the max (recommended) size of a texture is 256x256.... Should I just accept this (and scale the image when it comes to render time), or should I use a surface instead? (Is there any way to alpha blend surfaces?)

Or... alternatively, am I being a total idiot when there's a much easier (and less memory intensive-- 256 x 256 x 32 bit = huge bitmaps!) way to do this?? :P

thanks!

-maxthecat

First of all you need to use a texture size of a power of 2. If you don't DirectX will still create one for you, this you are wasting texture space by not using the leftovers.

Try it. Create a texture that is 125x123 and then retrieve the SurfaceDesc for it. It will be 128x128.

Your problem can be solved by creating meshes for each country and setting the diffuse material color to the color of the country when you click on it. The click could be attained by ray picking or casting a ray into 3D space and seeing what it hits.

For 2D, you would need to have alpha maps and/or diffuse maps for each country.

Interesting... Yeah, it's a 2D app.... I've been blitting the background bitmap onto a surface (the entire image was never fully displayed), and I was planning on using textures to act as the highlighting....

Alpha maps eh? How does that work? I couldn't find that mentioned in the SDK, or on these boards. Any links you have (or good books that you reccommend) would be more than appreiciated

After a bit more 'o research, the only thing I've found resembling 'alpha maps' is alpha blending... That wouldn't be a problem with this, except for the countries that are greater than 256 pixels in any direction.

Do you think I should break up the countries into mulitple textures for ones that are bigger than 256px, or would it be better to simply live with the scaling that occurs when a texture is applied to a primitive that's bigger than 256 x 256?

Also, with 75 countries, isn't having 18.75 MB (256 * 256 * 32 * 75 bits) worth of bitmaps just for highlighting a bit extreme?

The 256x256 limit is totally dependent on the card you have. Most modern cards support texture sizes of 1024x1024 and greater with no problem.

Interesting! Thanks for the help guys!

Code:

struct CountryVertex
{
  D3DVECTOR3 Pos;
  D3DCOLOR Diffuse;
  D3DCOLOR Specular;
  float tu,tv;
 
  static const DWORD FVF;
  CountryVertex(void):Pos(D3DXVECTOR3(0.0f,0.0f,0.0f),Diffuse(0),Specular(0),tu(0.0f),tv(0.0f) {}
  CountryVertex(D3DXVECTOR3 _Pos,float u,float v):Pos(_Pos),tu(y),tv(v) {}
};
  

class Country
{
  ID3DMESH9 *m_pMesh;
  D3DXVECTOR3 Pos;
  D3DMATERIAL9 m_pMaterial;
  
  public:
    Country(void):m_pMesh(NULL),Pos(&D3DXVECTOR3(0.0f,0.0f,0.0f)) {}

    void Create(IDirect3DDevice9 *pDevice);
    ...
};

Something like that would work for starters. Each country is a mesh of it's own and to change the color of it you simply change the material property of the mesh.