feat(demos): added heart demo by @turgenevivan

Closes #19 which has been turned into discussion #21

.editorconfig

@@ -30,4 +30,5 @@ max_line_length = 120
 # See: https://github.com/CppCXY/EmmyLuaCodeStyle/blob/master/docs/format_config_EN.md
 quote_style                       = single
 trailing_table_separator          = smart
+align_function_params             = false
 align_continuous_assign_statement = false

demos/heart.lua

@@ -0,0 +1,179 @@
+-- Heart Demo by turgenevivan
+-- https://github.com/turgenevivan
+
+local fenster = require('fenster')
+
+local width = 144
+local height = 144
+local window_scale = 4
+local fps = 30
+
+local window = fenster.open(width, height, 'Heart Demo - Press ESC to exit, 1-4 to change type', window_scale, fps)
+
+-- Heart shape function
+local function heart(x, y)
+	-- https://mathworld.wolfram.com/HeartCurve.html
+	-- Convert window coordinates to mathematical coordinates, using window center as origin
+	local xp = (x - width / 2) / (width / 3) -- Scale factor for x
+	local yp = (height / 2 - y) / (height / 3) -- Scale and invert y because y increases downwards
+
+	-- Heart equation: (x^2 + y^2 - 1)^3 = x^2 * y^3
+	return (xp ^ 2 + yp ^ 2 - 1) ^ 3 - xp ^ 2 * yp ^ 3 <= 0
+end
+
+-- Define the heart shape function with a pattern using level sets
+local function heart_with_pattern(x, y)
+	-- https://en.wikipedia.org/wiki/Level_set
+	-- Convert window coordinates to mathematical coordinates, using window center as origin
+	local xp = (x - width / 2) / (width / 3) -- Scale factor for x
+	local yp = (height / 2 - y) / (height / 3) -- Scale and invert y
+
+	-- Heart level set function
+	local z = xp * xp + yp * yp - 1
+	local f = z * z * z - xp * xp * yp * yp * yp
+
+	-- Mapping result to color intensity (like characters in the original code)
+	if f <= 0.0 then
+		-- Map 'f' value to grayscale intensity based on the same idea as character mapping
+		local intensity = math.floor((f * -8.0) % 8) -- Same concept as indexing into characters
+		local shades = {
+			0x330000,          -- Dark red (represents '@')
+			0x660000,          -- Darker red (represents '%')
+			0x990000,          -- Medium dark red (represents '#')
+			0xcc0000,          -- Medium red (represents '*')
+			0xff0000,          -- Bright red (represents '+')
+			0xff3333,          -- Light red (represents '=')
+			0xff6666,          -- Lighter red (represents ':')
+			0xffffff,          -- White (represents '.')
+		}
+		return shades[intensity + 1] -- Return color based on intensity
+	else
+		return 0xffffff        -- Background white
+	end
+end
+
+-- Define the heart shape function f(x, y, z)
+local function f(x, y, z)
+	local a = x * x + (9.0 / 4.0) * y * y + z * z - 1
+	return a * a * a - x * x * z * z * z - (9.0 / 80.0) * y * y * z * z * z
+end
+
+-- Define h(x, z) function to find the surface at a given x and z
+local function h(x, z)
+	for y = 1.0, 0.0, -0.001 do
+		if f(x, y, z) <= 0.0 then
+			return y
+		end
+	end
+	return 0.0
+end
+
+
+local function draw_heart_with_pattern()
+	for x = 0, width - 1 do
+		for y = 0, height - 1 do
+			local color = heart_with_pattern(x, y)
+			window:set(x, y, color) -- Set pixel color based on the level set function using hex
+		end
+	end
+end
+
+local function draw_heart()
+	for x = 0, width - 1 do
+		for y = 0, height - 1 do
+			if heart(x, y) then
+				window:set(x, y, 0xff0000) -- Set red color for the heart shape
+			end
+		end
+	end
+end
+
+local function draw_heart3d()
+	for sy = 0, height - 1 do       -- same
+		local z = 1.5 - sy * 3.0 / height -- Map screen coordinates to z
+		for sx = 0, width - 1 do
+			local x = sx * 3.0 / width - 1.5 -- Map screen coordinates to x
+			local v = f(x, 0.0, z)  -- Evaluate the heart equation
+			local r = 0             -- Red channel value
+
+			if v <= 0.0 then
+				local y0 = h(x, z)                          -- Get the y value at (x, z)
+				local ny = 0.0011                           -- Small offset for normal calculation
+				local nx = h(x + ny, z) - y0                -- Calculate the normal x component
+				local nz = h(x, z + ny) - y0                -- Calculate the normal z component
+				local nd = 1.0 / math.sqrt(nx * nx + ny * ny + nz * nz) -- Normalize
+				local d = (nx + ny - nz) * nd * 0.5 + 0.5   -- Calculate brightness
+				r = math.floor(d * 255.0)                   -- Map to 0-255 range
+			end
+
+			-- Ensure red channel is clamped between 0 and 255
+			r = math.max(0, math.min(255, r))
+
+			-- Set the pixel color (R, G, B)
+			window:set(sx, sy, (r * 2 ^ 16) + (0 * 2 ^ 8) + 0) -- Only red color
+		end
+	end
+end
+
+-- Draw the heart shape with color
+local function draw_heart3d_animate(t)
+	-- Heart scaling based on time (to create the pulsing effect)
+	local s = math.sin(t)
+	local a = s * s * s * s * 0.2 -- Scaling factor based on sine wave
+
+	for sy = 0, height - 1 do
+		local z = 1.5 - sy * 3.0 / height -- Map screen coordinates to z
+		z = z * (1.2 - a)           -- animate
+		for sx = 0, width - 1 do
+			local x = sx * 3.0 / width - 1.5 -- Map screen coordinates to x
+			x = x * (1.2 + a)       -- animate
+			local v = f(x, 0.0, z)  -- Evaluate the heart equation
+			local r = 0             -- Red channel value
+
+			if v <= 0.0 then
+				local y0 = h(x, z)                          -- Get the y value at (x, z)
+				local ny = 0.0011                           -- Small offset for normal calculation
+				local nx = h(x + ny, z) - y0                -- Calculate the normal x component
+				local nz = h(x, z + ny) - y0                -- Calculate the normal z component
+				local nd = 1.0 / math.sqrt(nx * nx + ny * ny + nz * nz) -- Normalize
+				local d = (nx + ny - nz) * nd * 0.5 + 0.5   -- Calculate brightness
+				r = math.floor(d * 255.0)                   -- Map to 0-255 range
+			end
+
+			-- Ensure red channel is clamped between 0 and 255
+			r = math.max(0, math.min(255, r))
+
+			-- Set the pixel color (R, G, B)
+			local color = fenster.rgb(r, 0, 0)
+			window:set(sx, sy, color) -- Only red color
+		end
+	end
+end
+
+
+local draw_menu = {
+	[1] = draw_heart,
+	[2] = draw_heart_with_pattern,
+	[3] = draw_heart3d,
+	[4] = draw_heart3d_animate,
+}
+local draw_type = 1
+
+local t = 0
+while window:loop() and not window.keys[27] do
+	window:clear()
+
+	if window.keys[string.byte('1')] then
+		draw_type = 1
+	elseif window.keys[string.byte('2')] then
+		draw_type = 2
+	elseif window.keys[string.byte('3')] then
+		draw_type = 3
+	elseif window.keys[string.byte('4')] then
+		t = 0
+		draw_type = 4
+	end
+
+	draw_menu[draw_type](t)
+	t = t + 3 * window.delta -- Update time
+end