DX9 and textures

[Auraomega]

Currently in the process of 'learning' D3D, however I've stumbled across a small issue that I can't seem to figure out. I'm trying to load an image file which contains multiple textures (think of a tile sheet), and draw one of those textures, I can do it however it's a really unsightly method and I'm guessing there has to be something easier that I haven't managed to find.

This is my code basically:

void blitD3D(IDirect3DTexture9 *texture, RECT *rDest, D3DCOLOR vertexColour, float rotate)
{
	TLVERTEX *vertices;

	//lock the vertex buffer so only this thread can access it
	vertexBuffer->Lock(0, 0, (void**)&vertices, NULL);

	//vertices go clockwise
	vertices[0].colour = vertexColour;
	vertices[0].x = (float) rDest->left - 0.5f;
	vertices[0].y = (float) rDest->top - 0.5f;
	vertices[0].z = 0.0f;
	vertices[0].rhw = 1.0f;
	vertices[0].u = 0.0f;
	vertices[0].v = 0.0f;

	vertices[1].colour = vertexColour;
	vertices[1].x = (float) rDest->right - 0.5f;
	vertices[1].y = (float) rDest->top - 0.5f;
	vertices[1].z = 0.0f;
	vertices[1].rhw = 1.0f;
	vertices[1].u = 1.0f;
	vertices[1].v = 0.0f;

	vertices[2].colour = vertexColour;
	vertices[2].x = (float) rDest->right - 0.5f;
	vertices[2].y = (float) rDest->bottom - 0.5f;
	vertices[2].z = 0.0f;
	vertices[2].rhw = 1.0f;
	vertices[2].u = 1.0f;
	vertices[2].v = 1.0f;

	vertices[3].colour = vertexColour;
	vertices[3].x = (float) rDest->left - 0.5f;
	vertices[3].y = (float) rDest->bottom - 0.5f;
	vertices[3].z = 0.0f;
	vertices[3].rhw = 1.0f;
	vertices[3].u = 0.0f;
	vertices[3].v = 1.0f;

	if(rotate)
	{
		//rotation code here
	}

	//unlock the vertex buffer for external use
	vertexBuffer->Unlock();

	d3ddev->SetTexture(0, texture);

	d3ddev->DrawPrimitive(D3DPT_TRIANGLEFAN, 0, 2);
}

Now using the example of a 1024x1024 image which contains 4 textures of 512x512 each, I could change the u and v (my texture coordinates) to be u = 0.0f and v = 0.5f to load the top left corner of the second image, however this is going to become complex and erroneous if I start using say 3 images (0.333333333f anyone?), so is there something more friendly I can use than this?

 

[UncleRuckus]

Arrays are your friend, my friend

 

[Auraomega]

Maybe my brain is just having a slow day, but how will that help? I'm still going to be working with annoying numbers as opposed to coordinates unless I'm overlooking something blindly obvious.

 

[sirlemonhead]

You'll always want to know how many tiles you have per texture I guess?

Plus, the size of each tile, and size of the texture

const int tileWidth = 512;
const int tileHeight = 512;

const int textureWidth = 1024;
const int textureHeight = 1024;

// find out how big a single pixel is in terms of a float value 0.0 - 1.0
float RecipW = 1.0f / textureWidth;
float RecipH = 1.0f / textureHeight;

Then you'll be able to easily just specify offsets in terms of pixels into the texture.

So say you want to use what's effectively the bottom left tile in a 4x4 arrangement, just do:

// top left vertex
vertices[0].u = 0.0f; //we're bottom left so don't offset into the x position
vertices[0].v = (float)(tileHeight) * RecipH; // we're offset down one tile on the Y, so increment by tile height

// top right vertex
vertices[1].u = (float)(tileWidth) * RecipW; //we're skipping across by the width of the tile
vertices[1].v = (float)(tileHeight) * RecipH; // we're offset down one tile on the Y, so increment by tile height

lets say we want bottom right tile..

// top left vertex
vertices[0].u = (float)(tileWidth) * RecipW; //we're bottom right so offset across x by size of one tile
vertices[0].v = (float)(tileHeight) * RecipH; // we're offset down one tile on the Y, so increment by tile height

I think that's right..sorry if it's not explained well. Is this for animation or are you just trying to create a texture atlas?

 

[Auraomega]

Ah right, I see how that'd work. Also although I do know the image dimensions they will probably vary (so not able to hard code) and I hate having lots of arguments in my prototypes, but flicking through the DX documentation there's the option to store image data in a struct and read back dimensions from there, which is what I did to make things easier.

Anyway since doing this I've come to realise my classes are becoming increasingly more complex and awkward, so before I go ahead and use/change my current classes, is there a way to load only a certain set of coordinates from a file as a texture? D3DXCreateTextureFromFileEx allows me to specify the width and heigh in pixels, however this is from (0,0) and unfortunately there doesn't appear to be a way to change the origin, is there a similar function which would allow me to do this? If there is, it'd make things a hell of a lot easier for me however I'm not familiar with the majority of functions available to me.

EDIT: Disregard this, I really was having a slow day, I've sorted out my classes now into a structured layout.