feat: add rhodonea curve demo (#12)

* feat: add rhodonea curve demo

* add credits header

* update for v0.4.0

demos/rhodena-curve.lua

@@ -0,0 +1,97 @@
+-- Rhodonea Curves by Jakob Kruse
+-- /~https://github.com/jakob-kruse
+-- You can read more here https://en.wikipedia.org/wiki/Rose_(mathematics)
+
+local fenster = require("fenster")
+
+local windowSize = 900
+local window = fenster.open(windowSize, windowSize, "Math Roses - R to reset + ESC to exit", 1, 0)
+
+local function generateRoseValue(delta, variant)
+    return 100 * math.sin(variant(delta))
+end
+
+local function drawRose(window, offsetX, offsetY, delta, variant, generator)
+    local radius = generator(delta, variant)
+    local x = math.floor(radius * math.cos(delta) + offsetX)
+    local y = math.floor(radius * math.sin(delta) + offsetY)
+
+    x = math.max(0, math.min(windowSize - 1, x))
+    y = math.max(0, math.min(windowSize - 1, y))
+
+    window:set(x, y, 0xffffff)
+end
+
+local variantValues = {
+    -- Circle
+    function(delta)
+        return delta / delta
+    end,
+
+    -- 4-leaf rose
+    function(delta)
+        return math.sin(delta * 2)
+    end,
+
+    -- 12-leaf rose
+    function(delta)
+        return math.sin(delta * 6)
+    end,
+
+    -- Butterfly
+    function(delta)
+        return math.sin(delta) + math.sin(delta * 4)
+    end,
+
+    -- Biker Glasses
+    function(delta)
+        return math.sin(delta) + math.sin(delta * 3)
+    end,
+
+    -- Neutron Star
+    function(delta)
+        return math.tan(delta)
+    end,
+
+    -- Logarithmic Spiral
+    function(delta)
+        return math.log(delta)
+    end,
+
+    function(delta)
+        return math.rad(delta) * 10
+    end,
+
+    function(delta)
+        return math.fmod(delta, 2)
+    end
+}
+
+local gridSize = math.ceil(math.sqrt(#variantValues))
+local cellSize = windowSize / gridSize
+local delta = 0
+
+while window:loop() and not window.keys[27] do
+    if window.keys[82] then
+        delta = 0
+        window:clear()
+    end
+
+    for i = 0, gridSize - 1 do
+        for j = 0, gridSize - 1 do
+            local variant = variantValues[i * gridSize + j + 1]
+            if variant then
+                drawRose(
+                    window,
+                    i * cellSize + cellSize / 2,
+                    j * cellSize + cellSize / 2,
+                    delta,
+                    variant,
+                    generateRoseValue
+                )
+            end
+        end
+    end
+
+    delta = delta + 0.0005
+end