1 files changed, 104 insertions, 0 deletions
diff --git a/libs/moonshine/glow.lua b/libs/moonshine/glow.lua
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+++ b/libs/moonshine/glow.lua
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+--[[
+Public domain:
+
+Copyright (C) 2017 by Matthias Richter <vrld@vrld.org>
+
+Permission to use, copy, modify, and/or distribute this software for any
+purpose with or without fee is hereby granted.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+PERFORMANCE OF THIS SOFTWARE.
+]]--
+
+
+-- unroll convolution loop for gaussian blur shader
+local function make_blur_shader(sigma)
+  local support = math.max(1, math.floor(3*sigma + .5))
+  local one_by_sigma_sq = sigma > 0 and 1 / (sigma * sigma) or 1
+  local norm = 0
+
+  local code = {[[
+    extern vec2 direction;
+    vec4 effect(vec4 color, Image texture, vec2 tc, vec2 _) {
+      vec4 c = vec4(0.0);
+  ]]}
+  local blur_line = "c += vec4(%f) * Texel(texture, tc + vec2(%f) * direction);"
+
+  for i = -support,support do
+    local coeff = math.exp(-.5 * i*i * one_by_sigma_sq)
+    norm = norm + coeff
+    code[#code+1] = blur_line:format(coeff, i)
+  end
+
+  code[#code+1] = ("return c * vec4(%f) * color;}"):format(1 / norm)
+
+  return love.graphics.newShader(table.concat(code))
+end
+
+return function(moonshine)
+  local blurshader -- set in setters.glow_strength
+  local threshold = love.graphics.newShader[[
+    extern number min_luma;
+    vec4 effect(vec4 color, Image texture, vec2 tc, vec2 _) {
+      vec4 c = Texel(texture, tc);
+      number luma = dot(vec3(0.299, 0.587, 0.114), c.rgb);
+      return c * step(min_luma, luma) * color;
+    }]]
+
+  local setters = {}
+  setters.strength = function(v)
+    blurshader = make_blur_shader(math.max(0,tonumber(v) or 1))
+  end
+  setters.min_luma = function(v)
+    threshold:send("min_luma", math.max(0, math.min(1, tonumber(v) or 0.5)))
+  end
+
+  local scene = love.graphics.newCanvas()
+  local draw = function(buffer)
+    local front, back = buffer() -- scene so far is in `back'
+    scene, back = back, scene    -- save it for second draw below
+
+    -- 1st pass: draw scene with brightness threshold
+    love.graphics.setCanvas(front)
+    love.graphics.clear()
+    love.graphics.setShader(threshold)
+    love.graphics.draw(scene)
+
+    -- 2nd pass: apply blur shader in x
+    blurshader:send('direction', {1 / love.graphics.getWidth(), 0})
+    love.graphics.setCanvas(back)
+    love.graphics.clear()
+    love.graphics.setShader(blurshader)
+    love.graphics.draw(front)
+
+    -- 3nd pass: apply blur shader in y and draw original and blurred scene
+    love.graphics.setCanvas(front)
+    love.graphics.clear()
+
+    -- original scene without blur shader
+    love.graphics.setShader()
+    love.graphics.setBlendMode("add", "premultiplied")
+    love.graphics.draw(scene) -- original scene
+
+    -- second pass of light blurring
+    blurshader:send('direction', {0, 1 / love.graphics.getHeight()})
+    love.graphics.setShader(blurshader)
+    love.graphics.draw(back)
+
+    -- restore things as they were before entering draw()
+    love.graphics.setBlendMode("alpha", "premultiplied")
+    scene = back
+  end
+
+  return moonshine.Effect{
+    name = "glow",
+    draw = draw,
+    setters = setters,
+    defaults = {min_luma=.7, strength = 5}
+  }
+end