Decal on texture

Try this code. You just need to call:

ApplyDecal source_texture , dest_texture [,r,g,b]

Both 'texture' parameters should point to a loaded texture.
The source texture is the DECAL and the destination texture is where the decal is applied.
The optional rgb flags are used for masking the decal.
In the example below the decals background is masked out using 255,0,255

The two test images I used:

; Applying a DECAL to a texture
; Syntax Error

Graphics3D 640,480
SetBuffer BackBuffer()
cam=CreateCamera() : light=CreateLight()
cube=CreateCube() : MoveEntity cube,0,0,4
cubetex=LoadTexture("wood.jpg")
EntityTexture cube,cubetex

decal=LoadTexture("decal.png")

Repeat
	TurnEntity cube,0.5,0.6,0.7
	If KeyHit(57) ApplyDecal decal,cubetex ,255,0,255
	RenderWorld
	Text 10,10,"Press [SPACE] to apply the decal ..."
	Flip
Until KeyHit(1)
End


; Apply source texture to destination texture (with optional masking)
Function ApplyDecal(sourceb,destb,maskR=0,maskG=0,maskB=0)
	Local gb=GraphicsBuffer() , rgb
	Local sb=TextureBuffer(sourceb) , db=TextureBuffer(destb)
	Local maxw=TextureWidth(sourceb) , maxh=TextureHeight(sourceb)
	If TextureWidth(destb)<maxw Then maxw=TextureWidth(destb)
	If TextureHeight(destb)<maxh Then maxh=TextureHeight(destb)
	LockBuffer sb : LockBuffer db
	For x=0 To maxw-1
		For y=0 To maxh-1
			rgb=ReadPixelFast(x,y,sb) And $00FFFFFF
			If Not rgb=((maskR Shl 16)+(maskG Shl 8)+maskB)
				WritePixelFast x,y,(rgb Or $FF000000),db
			EndIf
		Next
	Next
	UnlockBuffer sb : UnlockBuffer db
	SetBuffer gb
End Function