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+/*
+  Copyright 2019-2020 David Robillard <http://drobilla.net>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THIS 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.
+*/
+
+/**
+   @file rects.h Utilities for rectangle animation demos.
+
+   This file contains common definitions for demos that show an animation of
+   many 2D rectangles.
+*/
+
+#include <math.h>
+#include <stddef.h>
+
+typedef float vec2[2];
+
+typedef struct {
+	float pos[2];
+	float size[2];
+	float fillColor[4];
+} Rect;
+
+static const vec2 rectVertices[] = {
+    {0.0f, 0.0f}, // TL
+    {1.0f, 0.0f}, // TR
+    {0.0f, 1.0f}, // BL
+    {1.0f, 1.0f}  // BR
+};
+
+static const unsigned rectIndices[4] = {0, 1, 2, 3};
+
+/// Make a new rectangle with the given index (each is slightly different)
+static inline Rect
+makeRect(const size_t index, const float frameWidth)
+{
+	static const float alpha   = 0.3f;
+	const float        minSize = frameWidth / 64.0f;
+	const float        maxSize = frameWidth / 6.0f;
+	const float        s       = (sinf((float)index) / 2.0f + 0.5f);
+	const float        c       = (cosf((float)index) / 2.0f + 0.5f);
+
+	const Rect rect = {
+	    {0.0f, 0.0f}, // Position is set later during expose
+	    {minSize + s * maxSize, minSize + c * maxSize},
+	    {0.0f, s / 2.0f + 0.25f, c / 2.0f + 0.25f, alpha},
+	};
+
+	return rect;
+}
+
+/// Move `rect` with the given index around in an arbitrary way that looks cool
+static inline void
+moveRect(Rect* const  rect,
+         const size_t index,
+         const size_t numRects,
+         const float  frameWidth,
+         const float  frameHeight,
+         const double time)
+{
+	const float normal    = index / (float)numRects;
+	const float offset[2] = {normal * 128.0f, normal * 128.0f};
+
+	rect->pos[0] = (frameWidth - rect->size[0] + offset[0]) *
+	               (sinf((float)time * rect->size[0] / 64.0f + normal) + 1.0f) /
+	               2.0f;
+	rect->pos[1] = (frameHeight - rect->size[1] + offset[1]) *
+	               (cosf((float)time * rect->size[1] / 64.0f + normal) + 1.0f) /
+	               2.0f;
+}