love.graphics.stencil

Available since LÖVE 0.10.0

Together with love.graphics.setStencilTest, it has replaced love.graphics.setStencil.

Draws geometry as a stencil.

The geometry drawn by the supplied function sets the invisible stencil values of pixels, instead of setting pixel colors. The stencil values of pixels can act like a mask / stencil - love.graphics.setStencilTest can be used afterward to determine how further rendering is affected by the stencil values in each pixel.

Each Canvas has its own per-pixel stencil values. Stencil values are within the range of [0, 255].

Function

Synopsis

love.graphics.stencil( stencilfunction, action, value, keepvalues )

Arguments

function stencilfunction

Function which draws geometry. The stencil values of pixels, rather than the color of each pixel, will be affected by the geometry.

StencilAction action ("replace")

How to modify any stencil values of pixels that are touched by what's drawn in the stencil function.

number value (1)

The new stencil value to use for pixels if the "replace" stencil action is used. Must be between 0 and 255.

boolean keepvalues (false)

True to preserve old stencil values of pixels, false to re-set every pixel's stencil value to 0 before executing the stencil function. love.graphics.clear will also re-set all stencil values.

Returns

Nothing.

Examples

Drawing circles masked by a rectangle

local function myStencilFunction()
   love.graphics.rectangle("fill", 225, 200, 350, 300)
end

function love.draw()
    -- draw a rectangle as a stencil. Each pixel touched by the rectangle will have its stencil value set to 1. The rest will be 0.
    love.graphics.stencil(myStencilFunction, "replace", 1)

   -- Only allow rendering on pixels which have a stencil value greater than 0.
    love.graphics.setStencilTest("greater", 0)

    love.graphics.setColor(255, 0, 0, 120)
    love.graphics.circle("fill", 300, 300, 150, 50)

    love.graphics.setColor(0, 255, 0, 120)
    love.graphics.circle("fill", 500, 300, 150, 50)

    love.graphics.setColor(0, 0, 255, 120)
    love.graphics.circle("fill", 400, 400, 150, 50)

    love.graphics.setStencilTest()
end

Using an Image as a stencil mask

-- a black/white mask image: black pixels will mask, white pixels will pass.
local mask = love.graphics.newImage("mymask.png")

local mask_shader = love.graphics.newShader[[
   vec4 effect(vec4 color, Image texture, vec2 texture_coords, vec2 screen_coords) {
      if (Texel(texture, texture_coords).rgb == vec3(0.0)) {
         // a discarded pixel wont be applied as the stencil.
         discard;
      }
      return vec4(1.0);
   }
]]

local function myStencilFunction()
   love.graphics.setShader(mask_shader)
   love.graphics.draw(mask, 0, 0)
   love.graphics.setShader()
end

function love.draw()
    love.graphics.stencil(myStencilFunction, "replace", 1)
    love.graphics.setStencilTest("greater", 0)
    love.graphics.rectangle("fill", 0, 0, 256, 256)
    love.graphics.setStencilTest()
end

The love.graphics.setStencilTest wiki page includes more examples.

See Also

• love.graphics
• love.graphics.setStencilTest
• love.graphics.clear

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