I am currently working on a dynamic GUI system using C++ and DirectX. I have the majority of it planned out on paper, and am just starting to code it. I've gotten caught up in the discovery of D3DXFillTexture, which is what brought me here.

I may not be understanding how this works, but this is what I want to do and how I am attempting it. I could set the tones with these function calls (light grey in this example):

[source lang="c++"]VOID WINAPI ColorFillGrey (D3DXVECTOR4* pOut, const D3DXVECTOR2* pTexCoord, const D3DXVECTOR2* pTexelSize, LPVOID pData)
{
*pOut = D3DXVECTOR4(150, 150, 150, 255);
}

void Panel::Init(){
...
D3DXFillTexture (m_texture, ColorFillGrey, NULL))
...
}[/source]

This would fill my box with a light grey color. Then when I go to draw it, I would apply the color that the user chose for the Panel.
[source lang="c++"]// SpriteHandler is a LPD3DXSPRITE
g_engine->getSpriteHandler()->Draw( m_texture, &m_rect, NULL, NULL, m_bkgColor );[/source]

The MSDN describes this color (5th) parameter as "The color and alpha channels are modulated by this value." This leads me to believe it will act as a "tint", but I may be way off. The reason I am trying to get this to work is that I would like to use different ColorFill functions depending on the algorithm I would like to apply, such as rounded corners, gradients, etc, then apply the desired color to those greyscale values.

What I am asking is "Am I understanding this correctly?" It seems like it should be working, but the square it draws is always a solid white, no matter what values I pass into the Vector4. Does anyone here have experience with this function that could share some insight? I see that it is used in shader stuff a lot, so maybe I'm going going deeper than I need to with this. Any other suggestions on how to make a dynamic Panel would be great as well.

If I can't get it to work, I go back to DrawPrimitive using TRIANGLELISTs to make colored rectangles, but it seems it would cut out the possibility of applying gradients, etc.

Color value parameters must be [0.f, 1.f] range.

Thank you, that's huge. I can get it to work fine to make the rectangle a solid color of any given tone, which is a nice step forward. However, when I tried a simple test, I could not get more than one color drawn on an image.
[source "c++"]VOID WINAPI ColorFillGrey (D3DXVECTOR4* pOut, const D3DXVECTOR2* pTexCoord,
const D3DXVECTOR2* pTexelSize, LPVOID pData)
{
float currentValue = 0;
if ( pTexCoord->y < 0.5f ) // if top half
currentValue = 255;
else // if bottom half
currentValue = 10;

*pOut = D3DXVECTOR4(currentValue / 255.f, currentValue / 255.f, currentValue / 255.f, 1.f);
}[/source]
This, I figured would give me a rectangle that is half and half white/dark, with the bottom half being the dark portion. I put some breakpoints and the if/else seems to be called at the right time, but the final rectangle rendered is completely the dark value. Any suggestions on where I went wrong? Finding documentation and/or samples of this has been nigh impossible.