resize helper for perspective

* when window resized we only change aspect ratio, so projection still
keeps same

include/cglm-cam.h

@@ -153,6 +153,18 @@ glm_perspective_default(mat4 dest) {
                   dest);
 }
 
+CGLM_INLINE
+void
+glm_perspective_resize(mat4 proj) {
+  int32_t rect[4];
+
+  if (proj[0][0] == 0)
+    return;
+
+  glm_platfom_get_viewport_rect(rect);
+  proj[0][0] = (float)proj[1][1] * rect[3] / rect[2];
+}
+
 CGLM_INLINE
 void
 glm_lookat(vec3 eye,