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Checking for texture transparency with resize


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#1 Alphablackwolf   Members   -  Reputation: 101

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Posted 02 May 2012 - 07:39 PM

Ok, so I was using the tutorial here: http://create.msdn.com/en-US/education/catalog/tutorial/collision_2d_perpixel

to figure out how to detect transparency on a texture (in my case, a button). What I want to do is to be able to detect if a point (mouse click) is on a transparent part of the texture or not. I think I understand how to do it for a texture normally, you get the texture's color data and find the point on the array created.

However I am trying to figure out how I could possibly do that with a texture I am drawing with rectangle bounds that shrink/grow the original image. Since the spritebatch draw routine takes the parameters for scaling/re-sizing, the texture2D object itself is not changed, and so there is no way I can find to get the color data for a re-sized texture. Here's the routine I have currently:

    Public Shared Function IsAtAlpha(textureToCheck As Texture2D, textureLocation As Rectangle, pointToCheck As Point) As Boolean
	    Dim colorData As Color()
	    colorData = New Color((textureToCheck.Width * textureToCheck.Height) - 1) {}
	    textureToCheck.GetData(colorData)
	    Dim SpecificPointColor As Color = colorData((pointToCheck.X - textureLocation.Left) +
												    (pointToCheck.Y - textureLocation.Top) * textureToCheck.Width)
	    Return SpecificPointColor.A = 0
    End Function

If I could get a resized texture2D object I know what to change to get this to work properly, but I have no clue how to get that. Or is there a better way to check for transparency here?

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#2 laztrezort   Members   -  Reputation: 950

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Posted 02 May 2012 - 10:27 PM

There may be an easier way, maybe an XNA guru here will give a better answer, but personally I would try and tackle this by adjusting your sample coordinates (array index) of the original texture by the scale factor. This may be innacurate unless you reproduce the sampling method used by the shader, however (IIRC mip-mapping is enabled by default)

Or, you could render to a rendertarget and query that - this might be slower, but if you aren't scaling the texture every frame it may work fine.

#3 Alphablackwolf   Members   -  Reputation: 101

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Posted 03 May 2012 - 11:58 AM

Thanks Laztrezort, I dived into some of that stuff, and I ALMOST have it... Unfortunately I am getting a purple block when trying to get a renderTarget2D Texture.

After looking around online I found a lot of issues with the renderTarget stuff, mostly about 1.0-2.0, which has all changed again in 4.0. I moved my render target code out of the draw event and tried to create a quick draw in the load event of the button, but now I'm getting no image whatsoever.. Here's what I currently have:

	Public Sub Load(Content As ContentManager) Implements IButton.Load
		texture = Content.Load(Of Texture2D)(_spriteAssetLocation)
		Dim tempGraphicsDevice As GraphicsDevice = texture.GraphicsDevice
		Dim tempSpriteBatch As New SpriteBatch(tempGraphicsDevice)
		Dim renderTarget As New RenderTarget2D(tempGraphicsDevice, Bounds.Width, Bounds.Height)
		tempGraphicsDevice.SetRenderTarget(renderTarget)
		tempSpriteBatch.Begin()
		tempSpriteBatch.Draw(texture, Bounds, Color.White)
		tempSpriteBatch.End()
		tempGraphicsDevice.SetRenderTarget(Nothing)
		scaledTexture = renderTarget
	End Sub

I figure if it's in the load event I only have to do it the once, then I'll have the scaled texture to compare against.


Edit: Sorry, the above code is giving me a purple square. I was getting nothing at all when I set up 'Preserve Usage,' but that's something I want to avoid doing now anyway.

Edit2: Got it. I was drawing the texture on the render target in a location that it was not viewable on. I set a newbounds rectangle with a location of (0,0) but the width/height of the bounds rectangle and used that in my call to draw the texture on my renderTarget. All working swimmingly now, and my check of texture transparency is working perfectly.

Edited by Alphablackwolf, 03 May 2012 - 12:55 PM.





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