From c63c6c90aceb7e8ead996775dc9c83f699f60514 Mon Sep 17 00:00:00 2001
From: Recep Aslantas <info@recp.me>
Date: Tue, 17 Apr 2018 11:12:18 +0300
Subject: [PATCH] implement rotate_at

---
 include/cglm/affine.h      | 24 ++++++++++++++++++++++--
 include/cglm/call/affine.h |  4 ++++
 src/affine.c               |  6 ++++++
 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/include/cglm/affine.h b/include/cglm/affine.h
index 10f190f..39c4290 100644
--- a/include/cglm/affine.h
+++ b/include/cglm/affine.h
@@ -400,7 +400,7 @@ glm_rotate_make(mat4 m, float angle, vec3 axis) {
 }
 
 /*!
- * @brief rotate existing transform matrix around Z axis by angle and axis
+ * @brief rotate existing transform matrix around given axis by angle
  *
  * this name may change in the future, axis must be normalized.
  *
@@ -439,7 +439,7 @@ glm_rotate_ndc(mat4 m, float angle, vec3 axis_ndc) {
 }
 
 /*!
- * @brief rotate existing transform matrix around Z axis by angle and axis
+ * @brief rotate existing transform matrix around given axis by angle
  *
  * @param[in, out]  m      affine transfrom
  * @param[in]       angle  angle (radians)
@@ -454,6 +454,26 @@ glm_rotate(mat4 m, float angle, vec3 axis) {
   glm_rotate_ndc(m, angle, axis_ndc);
 }
 
+/*!
+ * @brief rotate existing transform
+ *        around given axis by angle at given pivot point (rotation center)
+ *
+ * @param[in, out]  m      affine transfrom
+ * @param[in]       angle  angle (radians)
+ * @param[in]       axis   axis
+ */
+CGLM_INLINE
+void
+glm_rotate_at(mat4 model, vec3 pivot, float angle, vec3 axis) {
+  vec3 pivotInv;
+
+  glm_vec_inv_to(pivot, pivotInv);
+
+  glm_translate(model, pivot);
+  glm_rotate(model, angle, axis);
+  glm_translate(model, pivotInv);
+}
+
 /*!
  * @brief decompose scale vector
  *
diff --git a/include/cglm/call/affine.h b/include/cglm/call/affine.h
index 65dfae0..6d6b872 100644
--- a/include/cglm/call/affine.h
+++ b/include/cglm/call/affine.h
@@ -85,6 +85,10 @@ CGLM_EXPORT
 void
 glmc_rotate(mat4 m, float angle, vec3 axis);
 
+CGLM_EXPORT
+void
+glmc_rotate_at(mat4 model, vec3 pivot, float angle, vec3 axis);
+
 CGLM_EXPORT
 void
 glmc_decompose_scalev(mat4 m, vec3 s);
diff --git a/src/affine.c b/src/affine.c
index 056947f..793d8ee 100644
--- a/src/affine.c
+++ b/src/affine.c
@@ -116,6 +116,12 @@ glmc_rotate(mat4 m, float angle, vec3 axis) {
   glm_rotate(m, angle, axis);
 }
 
+CGLM_EXPORT
+void
+glmc_rotate_at(mat4 model, vec3 pivot, float angle, vec3 axis) {
+  glm_rotate_at(model, pivot, angle, axis);
+}
+
 CGLM_EXPORT
 void
 glmc_decompose_scalev(mat4 m, vec3 s) {