[core] allow changing the orientation

You can now change the orientation of north to be to the right, bottom, left in addition to the default of top

1 files changed, 34 insertions, 0 deletions

diff --git a/src/mbgl/util/mat4.cpp b/src/mbgl/util/mat4.cpp
index 0934cd081e..5f6f9d1b4c 100644
--- a/src/mbgl/util/mat4.cpp
+++ b/src/mbgl/util/mat4.cpp
@@ -214,6 +214,40 @@ void matrix::rotate_x(mat4& out, const mat4& a, double rad) {
     out[11] = a23 * c - a13 * s;
 }
 
+void matrix::rotate_y(mat4& out, const mat4& a, double rad) {
+    double s = std::sin(rad),
+        c = std::cos(rad),
+        a00 = a[0],
+        a01 = a[1],
+        a02 = a[2],
+        a03 = a[3],
+        a20 = a[8],
+        a21 = a[9],
+        a22 = a[10],
+        a23 = a[11];
+
+    if (&a != &out) { // If the source and destination differ, copy the unchanged rows
+        out[4]  = a[4];
+        out[5]  = a[5];
+        out[6]  = a[6];
+        out[7]  = a[7];
+        out[12] = a[12];
+        out[13] = a[13];
+        out[14] = a[14];
+        out[15] = a[15];
+    }
+
+    // Perform axis-specific matrix multiplication
+    out[0] = a00 * c - a20 * s;
+    out[1] = a01 * c - a21 * s;
+    out[2] = a02 * c - a22 * s;
+    out[3] = a03 * c - a23 * s;
+    out[8] = a00 * s + a20 * c;
+    out[9] = a01 * s + a21 * c;
+    out[10] = a02 * s + a22 * c;
+    out[11] = a03 * s + a23 * c;
+}
+
 void matrix::rotate_z(mat4& out, const mat4& a, double rad) {
     double s = std::sin(rad),
           c = std::cos(rad),