LÖVE

Code: Select all

local shader

-- call once per program run
function InitShader()
	local pixelcode = [[
		extern vec2 shift;
		extern Image eraser;

		vec4 effect(vec4 color, Image texture, vec2 tc, vec2 sc)
		{
			vec4 texturePixel = Texel(texture, tc);
			vec4 eraserPixel = Texel(texture, tc + shift);
			texturePixel.a = texturePixel.a * (1.0f - eraserPixel.a);
			return texturePixel;
		}
	]]

	shader = love.graphics.newShader(pixelcode)
end

-- call once for change eraser texture
function SetEraserTexture(eraser)
	shader:send("eraser", eraser)
end

-- call every time you want to move eraser, i.e. every frame
function SetEraserShift(shift)
	shader:send("shift", shift)
end

Code: Select all

--this shader substracts alpha of the eraser brush
--offset calculation still incorrect

function love.load()

	offset={}
	offset.x=400.0
	offset.y=400.0

	circle=love.graphics.newImage('circle.png')

	cvs1=love.graphics.newCanvas(640,480)
	love.graphics.setCanvas(cvs1)
	--first canvas is filled with redmod
	love.graphics.clear(1.0,0.0,0.0,1.0)

	--the canvas holding the real image data
	curcvs=cvs1

	
	cvs2=love.graphics.newCanvas(640,480)
	love.graphics.setCanvas(cvs2)
	love.graphics.clear(0.0,0.0,0.0,0.0)

	backcvs=cvs2 -- the back buffer the frag shader will render to

	love.graphics.setCanvas()

	local pixelcode=[[
		//second is the eraser
		extern Image second;
		extern float cvsw;
		extern float brshw;
		extern float cvsh;
		extern float brshh;
		extern float offx;//pixels
		extern float offy;//pixels

		vec4 effect(vec4 color,Image texture,vec2 tc,vec2 sc){
			
			
			float pxw=1.0 / brshw;
			float pxh=1.0/brshh;
			
			
			vec4 texturePixel=Texel(texture,tc);
			
			
			float tcx = tc.x*cvsw/brshw-offx*pxw;
			if (tcx>1.0 || tcx<0.0 ){
				return texturePixel;
			}
			float tcy = tc.y*cvsh/brshh-offy*pxh;
			if (tcy>1.0 || tcy<0.0){
				return texturePixel;
			}
			vec2 rtc=vec2(tcx,tcy);
			
			vec4 secondPixel=Texel(second,rtc);
			
				vec4 ret=texturePixel ;
				ret.a=ret.a-secondPixel.a;
				return ret;
			
		}
	]]
	
	shader=love.graphics.newShader(pixelcode)

	shader:send("second",circle)
	shader:send("cvsw",640.0)
	shader:send("brshw",64.0)
	shader:send("cvsh",480.0)
	shader:send("brshh",64.0)
	shader:send("offx",offset.x)
	shader:send("offy",offset.y)

	--test erase from curcvs to backcvs
	love.graphics.setCanvas(backcvs)
	love.graphics.setShader(shader)
	love.graphics.draw(curcvs)
	love.graphics.setShader()
	love.graphics.setCanvas()

end


function love.draw()

	love.graphics.draw(backcvs)
	love.graphics.print('eraser shader test')


end