1 files changed, 38 insertions, 0 deletions
diff --git a/scale.cpp b/scale.cpp
new file mode 100644
index 0000000..ba0cff0
--- /dev/null
+++ b/scale.cpp
@@ -0,0 +1,38 @@
+#include "scale.h"
+
+#include <iostream>
+
+void updateTransform4x4(const LinearScale<float> &sx,
+                        const LinearScale<float> &sy,
+                        float transform[4][4])
+{
+    float fsx = 2.0f * sx.slope();
+    float ftx = 2.0f * sx.offset() - 1.0f;
+    float fsy = 2.0f * sy.slope();
+    float fty = 2.0f * sy.offset() - 1.0f;
+
+    // The transform matrix should be this, but we have it transposed
+    // in memory:
+    //
+    // [   sx  0.0f  0.0f    tx ]
+    // [ 0.0f    sy  0.0f    ty ]
+    // [ 0.0f  0.0f  0.0f  0.0f ]
+    // [ 0.0f  0.0f  0.0f  1.0f ]
+    //
+    // It is already initialized with 0s and bottom-right 1
+    transform[0][0] = fsx;
+    transform[1][1] = fsy;
+    transform[3][0] = ftx;
+    transform[3][1] = fty;
+}
+
+void updateTransform4x4(LinearScale<float> &sx,
+                        LinearScale<float> &sy,
+                        float offsetX,
+                        float offsetY,
+                        float transform[4][4])
+{
+    sx.setRange(offsetX, 1.0f - offsetX);
+    sy.setRange(1.0f - offsetY, offsetY);
+    updateTransform4x4(sx, sy, transform);
+}