texture utilities including various downsamples, dilation, and blurring

texture_utils.lua

--texture utilities
--todo: clean up and include in https://github.com/1bardesign/batteries

--[[

Copyright (c) 2020 Max Cahill

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
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The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
 

]]

local downsample_template = [[
uniform float scale_factor;
uniform vec2 big_res;
uniform vec2 small_res;
#ifdef PIXEL
vec4 effect(vec4 c, Image t, vec2 uv, vec2 px) {
	vec2 big_uv_origin_px = (floor(uv * small_res) / small_res) * big_res + vec2(0.5);
	vec4 accum = vec4(<init>);
	for (float oy = 0; oy < scale_factor; oy++) {
		for (float ox = 0; ox < scale_factor; ox++) {
			vec2 ouv = (big_uv_origin_px + vec2(ox, oy)) / big_res;
			vec4 px = Texel(t, ouv);
			<op>
		}
	}
	return <res>;
}
#endif
]]

local function create_downsample_shader(init, op, res)
	local src = downsample_template
	src = src:gsub("<init>", init)
	src = src:gsub("<op>", op)
	src = src:gsub("<res>", res)

	return lg.newShader(src)
end

local downsample_shaders = {
	average = create_downsample_shader(
		"0.0",
		"accum += px;",
		"accum / (scale_factor * scale_factor)"
	),
	min = create_downsample_shader(
		"100.0",
		"accum = min(accum, px);",
		"accum"
	),
	max = create_downsample_shader(
		"-100.0",
		"accum = max(accum, px);",
		"accum"
	),
}

function downsample_canvas(big, small, op)
	local shader = downsample_shaders[op]
	if not shader then
		error("unknown op for downsample_canvas, " .. tostring(op))
	end
	local scale_factor = math.ceil(big:getWidth() / small:getWidth())
	love.graphics.push("all")
	love.graphics.setCanvas(small)
	if scale_factor == 1 then
		--just copy
		love.graphics.setBlendMode("replace", "premultiplied")
		love.graphics.draw(big)
		love.graphics.pop()
		return
	end
	local downscale_factor = 1 / scale_factor
	shader:send("scale_factor", scale_factor)
	shader:send("big_res", {big:getDimensions()})
	shader:send("small_res", {small:getDimensions()})
	love.graphics.setShader(shader)
	love.graphics.draw(big, 0, 0, 0, downscale_factor, downscale_factor)
	love.graphics.pop()
end

local dilate_shader = lg.newShader([[
uniform vec2 res;
uniform float distance;
uniform bool do_min;
#ifdef PIXEL
vec4 effect(vec4 c, Image t, vec2 uv, vec2 px) {
	vec4 colour = Texel(t, uv);
	for (float oy = -distance; oy <= distance; oy++) {
		for (float ox = -distance; ox <= distance; ox++) {
			float a = 1.0;
			vec2 o = vec2(ox, oy);
			if (length(o) <= distance) {
				o /= res;
				if (do_min) {
					colour = min(colour, Texel(t, uv + o));
				} else {
					colour = max(colour, Texel(t, uv + o));
				}
			}
		}
	}
	return colour;
}
#endif
]])

function dilate_canvas(from, to, distance, do_min)
	dilate_shader:send("distance", distance)
	dilate_shader:send("res", {from:getDimensions()})
	dilate_shader:send("do_min", do_min)
	lg.push("all")
	lg.setCanvas(to)
	lg.setShader(dilate_shader)
	lg.draw(from)
	lg.pop()
	return to
end


local blur_shader = lg.newShader([[
uniform vec2 res;
uniform float steps;
uniform vec2 dimension;
uniform bool semi_gaussian;
#ifdef PIXEL
vec4 effect(vec4 c, Image t, vec2 uv, vec2 px) {
	vec4 colour = vec4(0.0);
	float total = 0.0;
	for (float oi = -steps; oi <= steps; oi++) {
		float a = 1.0;
		vec2 o = dimension * oi;
		if (semi_gaussian) {
			a = mix(1.0, 0.0, length(o) / (steps + 1.0));
		}
		if (a > 0) {
			o /= res;
			colour += Texel(t, uv + o) * a;
			total += a;
		}
	}
	return colour / total;
}
#endif
]])

function blur_canvas(from, partial, to, steps, semi_gaussian)
	blur_shader:send("steps", steps)
	blur_shader:send("res", {from:getDimensions()})
	blur_shader:send("semi_gaussian", semi_gaussian)
	lg.push("all")
	lg.setShader(blur_shader)
	blur_shader:send("dimension", {1, 0})
	lg.setCanvas(partial)
	lg.draw(from)
	blur_shader:send("dimension", {0, 1})
	lg.setCanvas(to)
	lg.draw(partial)
	lg.pop()
	return to
end