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// texture
uniform sampler2D texture0;
uniform sampler2D texture1;
varying vec2 uvVarying;

void main()
{
    vec4 basecolor = texture2D(texture0, uvVarying);
    vec4 overcolor = texture2D(texture1, uvVarying);
    
    //-- alpha blend
    float blendA = 1.0 - overcolor.a;
    float blendB = overcolor.a;
    //-- minus to erase
    gl_FragColor = (blendA * basecolor)-(blendB * overcolor);
}

HideAll() //Hide Ui and other layers
		
SetRenderToImage(Layer[LayerId].Img,0)	
// clearscreen()  // If I uncomment, it clear my layer at each frame
drawsprite(Brush)

CreateSprite(Layer[LayerId].Sprite,Layer[LayerId].Img)
UnHideAll() // Unhide all UI and other Layers

SetRenderToscreen()

HideAll() //Hide Ui and other layers
		
SetRenderToImage(Layer[LayerId].Img,0)	
SetClearColor(brush.colorR,Brush.colorG,brush.ColorB)  
drawsprite(Brush)

CreateSprite(Layer[LayerId].Sprite,Layer[LayerId].Img)
UnHideAll() // Unhide all UI and other Layers

SetRenderToscreen()

SetWindowTitle( "Eraser test" )
SetWindowSize( 1024, 768, 0 )
SetPrintSize(16)
SetClearColor(0,0,0)
ClearScreen()

// set display properties
SetVirtualResolution( 1024, 768 )

// load media
bg = LoadImage("bg.png")
brush = LoadImage("brush.png")
imgalpha = LoadImage("bg_alpha.png") // a simple white image with width and height the same as bg.png
// I will use this imgalpha as a mask (alpha chanel for image bg)

imgTemp = CopyImage(bg,0,0,GetImageWidth(bg),GetImageHeight(bg)) // for the temporary drawing



// create sprites
bgSpr = CreateSprite(bg)
SetSpriteSize(bg, 1024, 768)
SetSpritePosition(bgSpr, 0, 0)

BrushSpr = CreateSprite(brush)
SetSpritePosition(BrushSpr,-10000, 0)
SetSpriteColor(brushspr,0,0,0,255)


setSyncRate(10000, 0)
SetClearColor(100,100,100)
clearscreen()
do
	
	if GetPointerPressed()
		clic = 1
	elseif GetPointerReleased()
		clic = 0
		
		SetSpritePosition(brushspr,-10000,0)
		SetImageMask(bg,imgalpha,4,1,0,0)
		deletesprite(bgSpr)
		createsprite(bgSpr,bg)
		SetSpriteTransparency(bgspr,1)
		//SetSpritePosition(Bgspr,0,0)
		imgTemp = CopyImage(bg,0,0,GetImageWidth(bg),GetImageHeight(bg))
		
		
	endif
	
	X = GetPointerX()
	Y = GetPointerY()
	
	if clic = 1
		
		SetSpritePosition(Bgspr,-10000,0)
		
		setrendertoimage(imgalpha,0)
		setspriteposition(BrushSpr,x-64,y-64)
		drawsprite(brushspr)
		
		setrendertoimage(imgTemp,0)
		setspriteposition(BrushSpr,x-64,y-64)
		drawsprite(brushspr)
		
		SetRenderToScreen()
		deletesprite(bgspr)
		createsprite(bgSpr,imgTemp)
		SetSpriteTransparency(bgspr,1)
		SetSpritePosition(Bgspr,0,0)
		
	endif
	
	sync()
	Print("fps: " + str(ScreenFPS(), 0))
	
loop

// Settings
SetWindowTitle( "eraser shader" )
SetScreenResolution( 1280, 720)
SetSyncRate( 0, 0 )

SetVirtualResolution( 1280, 720 )
SetScissor( 0, 0, 0, 0 )

SetPrintSize(20)

Global w,h as integer
w = GetVirtualWidth()
h = GetVirtualHeight()


//load the shader.
global EraserShaderID as integer
EraserShaderID = LoadShader( "Quad.vs", "eraser.ps" )

// image & Layers
global LayerTotal as integer
LayerTotal = 1
CreateRenderImage( LayerTotal, w, h, 0, 0 )

global LayerActiv as integer
LayerActiv = 2
CreateRenderImage( LayerActiv, w, h, 0, 0 )

global TempLayer as integer // the temp image
TempLayer = 3
CreateRenderImage( TempLayer, w, h, 0, 0 )


//create Quad object to apply full screen shaders too
global ScreenObj as integer
ScreenObj = CreateObjectQuad()


//************** MEDIA LOADING
iBrush = 0
// iBrush = LoadImage( "brush.png" ) // here, load your own brush if needed
Global Brush as integer
Brush = CreateSprite(iBrush)
SetSpriteSize(brush,64,64)
SetSpriteOffset(brush, GetSpriteWidth(brush)/2,GetSpriteHeight(brush)/2)
SetSpriteColorAlpha(brush, 60)
SetSpritePosition(brush,-200,0)

Action = 0 // 0 = paint, 1 = eraser

SetClearColor(100,100,100)



//MAIN LOOP
repeat
    
	Print("FPS:"+str(ScreenFPS(),0) +" / Action : "+str(action))
    
    if GetPointerPressed()=1		
		oldx = ScreenToWorldX( GetPointerX() )
		oldy = ScreenToWorldY( GetPointerY() )
		ok = 1
	elseif GetPointerReleased()=1
		
		ok = 0	
		
		SetRenderToImage(TempLayer,0)
		ClearScreen()
		SetRenderToScreen()
		
		if action = 1
			SetSpriteTransparency(1,0)
			SetRenderToImage(LayerTotal,0)
			ClearScreen()			
		endif
		
		SetSpritePosition(1,0,0)
		SetRenderToImage(LayerTotal,0)
		DrawSprite(1)
		
		SetRenderToScreen()
		SetSpriteTransparency(1,1)
	   
		
	endif
	
	if GetPointerState()=1 and ok = 1
				
		x = ScreenToWorldX( GetPointerX() )
		y = ScreenToWorldY( GetPointerY() )
						
		
		if x <> oldx or y <> oldy
			if action = 0 // apint
				Paint(x,y)				
			else 
				erase(x,y)				
			endif
			oldx = x
			oldy = y
		endif
		
	endif
		
			
	if GetRawKeyReleased(65 ) = 1 // A
	    Action = 1-Action				
	Endif
	
	sync()
	
until GetRawKeyReleased( 27 )


// FUNCTION
function Paint(x,y)
	
	SetSpritePosition(1,-10000,0) // hide the layer activ to not draw it-self 
	
	SetRenderToImage( LayerActiv, 0 )
	SetSpritePositionByOffset(Brush,x,y)
	SetSpriteAngle(Brush,random(0,360))
	DrawSprite(Brush)
		
	CreateSprite(1,LayerActiv)
	SetSpriteTransparency(1,1)
	
	SetRenderToScreen()
    SetSpritePosition(1,0,0)
    
endfunction


Function Erase(x,y)
	
	SetSpritePosition(1,-10000,0)
	
	SetRenderToImage( TempLayer, 0 )	
	SetSpritePositionByOffset(Brush,x,y)
	SetSpriteAngle(Brush,random(0,360))
	DrawSprite(Brush)
	
	
	SetRenderToImage( LayerActiv,0)
	
    SetObjectImage( ScreenObj, LayerActiv, 0 )
    SetObjectImage( ScreenObj, TempLayer, 1 )
  
    SetObjectShader( ScreenObj, EraserShaderID )
	
	DrawObject( ScreenObj )
	
	DeleteSprite(1)
	CreateSprite(1,LayerActiv)
	SetSpriteTransparency(1,1)

	
	SetSpritePosition(1,0,0)
	
	 
	SetRenderToImage(TempLayer,0)	
	ClearScreen()
	
	
	SetRenderToScreen()
	
EndFunction

// Eraser shader from MATTY_H -AGK forum
// texture
uniform sampler2D texture0;
uniform sampler2D texture1;
varying vec2 uvVarying;

void main()
{
    vec4 basecolor = texture2D(texture0, uvVarying);
    vec4 overcolor = texture2D(texture1, uvVarying);
    
    //-- alpha blend
    float blendA = 1.0 - overcolor.a;
    float blendB = overcolor.a;
    //-- minus to erase
    gl_FragColor = (blendA * basecolor)-(blendB * overcolor);
	
	// tests
    // gl_FragColor = (blendA * overcolor)-(blendB * overcolor); // space
    // gl_FragColor = (blendA * basecolor) - (blendB * basecolor); // other eraser

	
}

attribute vec3 position;
attribute vec4 color;
attribute vec2 uv;

varying vec2 uvVarying;
varying vec2 posVarying;
varying vec4 colorVarying;
    
uniform vec4 uvBounds0; // to adjust for atlas sub images
uniform float agk_invert; // FBOs render upside down so flip the quad
    	
void main()
{
	gl_Position = vec4(position.xy*vec2(1,agk_invert),0.5,1.0);
	
	uvVarying = (position.xy*vec2(0.5,-0.5) + 0.5) * uvBounds0.xy + uvBounds0.zw;
	
	colorVarying = color;

}

// ERASER shader , By MATTY_H, modified by blendman
// texture
uniform sampler2D texture0;
uniform sampler2D texture1;
varying vec2 uvVarying;

void main()
{
    vec4 basecolor = texture2D(texture0, uvVarying);
    vec4 overcolor = texture2D(texture1, uvVarying);
    
    //-- alpha blend
    float blendA = 1.0 - overcolor.a;
    float blendB = overcolor.a;

    //-- minus to erase
    gl_FragColor.r = basecolor.r;
    gl_FragColor.g = basecolor.g;
    gl_FragColor.b = basecolor.b;
    gl_FragColor.a = (blendA * basecolor.a)-(blendB * overcolor.a);

    // gl_FragColor = (blendA * basecolor)-(blendB * overcolor); // old method
	
	
}

// texture
// Shader "keep alpha"
// Base MATTY_H from TGC forum, modified by blendman
uniform sampler2D texture0;
uniform sampler2D texture1;
varying vec2 uvVarying;

void main()
{
    vec4 basecolor = texture2D(texture0, uvVarying);
    vec4 overcolor = texture2D(texture1, uvVarying);
    
    //-- alpha blend
    float blendA = 1.0 - overcolor.a;
    float blendB = overcolor.a;
    
	//-- add to paint
    gl_FragColor.rgb = (blendA * basecolor.rgb)+(blendB * overcolor.rgb);   
    gl_FragColor.a = basecolor.a; // keep the alpha
    	
}