1 files changed, 39 insertions, 0 deletions
diff --git a/geometry.cpp b/geometry.cpp
new file mode 100644
index 0000000..3a4a861
--- /dev/null
+++ b/geometry.cpp
@@ -0,0 +1,39 @@
+#include "geometry.h"
+
+static const float PI = 3.1415f;
+
+int calculateCircleVertexCount(float radius)
+{
+    // 10 * sqrt(r) \approx 2*pi / acos(1 - 1 / (4*r))
+    return int(10.0 * sqrt(radius));
+}
+
+void updateCircleGeometry(QSGGeometry *geometry, float radius, float cx, float cy)
+{
+    int vertexCount = geometry->vertexCount();
+
+    float theta = 2 * PI / float(vertexCount);
+    float c = cosf(theta);
+    float s = sinf(theta);
+    float x = radius;
+    float y = 0;
+
+    QSGGeometry::Point2D *vertexData = geometry->vertexDataAsPoint2D();
+    for (int i = 0; i < vertexCount; i++) {
+        vertexData[i].set(x + cx, y + cy);
+
+        float t = x;
+        x = c*x - s*y;
+        y = s*t + c*y;
+    }
+}
+
+void updateRectGeometry(QSGGeometry *geometry, float x, float y, float w, float h)
+{
+    QSGGeometry::Point2D *vertexData = geometry->vertexDataAsPoint2D();
+
+    vertexData[0].set(x, y);
+    vertexData[1].set(x + w, y);
+    vertexData[2].set(x + w, y + h);
+    vertexData[3].set(x, y + h);
+}