Transforming texture coordinates

[markbiddlecom]

Hi, all!

This is what should be a relatively easy question (I hope). Ive got a texture loaded that contains several frames of an animation Id like to place on a sprite.

My vertex format is Position and Texture1, and is defined by the following structure:

[VB]
Public Structure Vertex
x As Single
y As Single
z As Single
tu As Single
tv As Single
End Structure
[/VB]

What Id like to be able to do is transform the texture coordinates in real-time to produce the animation effect.

So, my drawing code (very much abbreviated) looks like this (where m_buffer is a VertexBuffer object storing my sprite coordinates, and m_texture is an instance of the Texture class that contains the entire animation):

[VB]
Public Sub draw(ByVal device As Direct3D.Device)
device.VertexFormat = VertexFormats.Position Or _
VertexFormats.Texture1

device.SetTexture(0, m_texture)
device.TextureState(0).TextureTransform = _
TextureTransform.Count2

Transform the world coordinates
device.Transform.World = getSpriteMatrix()

Transform the texture coordinates
device.Transform.Texture0 = getTextureMatrix()

Draw.
device.DrawPrimitives(PrimitiveType.TriangleStrip, 0, 2)
End Sub

Private Function getTextureMatrix() As Matrix
Dim retVal As Matrix = Matrix.Identity

Determine the current frame...
<code removed>

retVal = Matrix.Multiply _
(retVal, _
Matrix.Scaling(curFrameWidth, curFrameHeight, 0) _
)

retVal = Matrix.Multiply _
(retVal, _
Matrix.Translation(curFrameLeft, curFrameTop, 0) _
)

Return retVal
End Function
[/VB]

Some more information: My vertex buffer contains four verticies, defined as such:

(0,0)
(1,0)
(0,1)
(1,1)

Note that all z values are zero, and that the tu and tv coordinates are identical to the x and y coordinates.

When I run the program, I notice that the texture coordinates properly scale, but they never seem to translate, and always anchor themselves to the texture origin.

I just now realized that I probably need to set the translation coordinates in the 3rd row instead of the 4th, since texture coordinates are 2D...

<edits code>

Well, that didnt work either: now, every other frame (when I perform the texture translation) I get a blank image, instead of my picture of water. Previously, I was just getting the same frame over and over.

The new code looks like this:

[VB]
Private Function getTextureMatrix() As Matrix
Dim retVal As Matrix = Matrix.Identity

Determine the current frame...
<code removed>

retVal = Matrix.Multiply _
(retVal, _
Matrix.Scaling(curFrameWidth, curFrameHeight, 0) _
)

retVal.M31 = curFrameLeft
retVal.M32 = curFrameTop

Return retVal
End Function
[/VB]

OK, so I still need help on how to properly translate texture coordinates.

Thanks in advance!

-Mark

 

[markbiddlecom]

Well, all, I seemed to have solved my own problem again

The issue had to do with the fact that I was actually multiplying the scaled texture matrix (in the getTextureMatrix function) by a new matrix returned by another function, get2DTranslationMatrix. That function returned a matrix with all zeros except for the M31 and M32 positions. So, naturally, when I multiplied it by the scaled matrix, the scale values went to 0.

Boy do I feel like an idiot

Thanks anyway!

-Mark