new project function for projecting Z

someitmes we need to project z only. this function reduces a few calculations and parameters.

include/cglm/call/project.h

@@ -25,6 +25,10 @@ CGLM_EXPORT
 void
 glmc_project(vec3 pos, mat4 m, vec4 vp, vec3 dest);
 
+CGLM_EXPORT
+float
+glmc_project_z(vec3 pos, mat4 m);
+
 CGLM_EXPORT
 void
 glmc_pickmatrix(vec2 center, vec2 size, vec4 vp, mat4 dest);

include/cglm/clipspace/project_no.h

@@ -83,4 +83,27 @@ glm_project_no(vec3 pos, mat4 m, vec4 vp, vec3 dest) {
   dest[2] = pos4[2];
 }
 
+/*!
+ * @brief map object's z coordinate to window coordinates
+ *
+ * Computing MVP:
+ *   glm_mat4_mul(proj, view, viewProj);
+ *   glm_mat4_mul(viewProj, model, MVP);
+ *
+ * @param[in]  v  object coordinates
+ * @param[in]  m  MVP matrix
+ *
+ * @returns projected z coordinate
+ */
+CGLM_INLINE
+float
+glm_project_z_no(vec3 v, mat4 m) {
+  float z, w;
+
+  z = m[0][2] * v[0] + m[1][2] * v[1] + m[2][2] * v[2] + m[3][2];
+  w = m[0][3] * v[0] + m[1][3] * v[1] + m[2][3] * v[2] + m[3][3];
+
+  return 0.5f * (z / w) + 0.5;
+}
+
 #endif /* cglm_project_no_h */

include/cglm/clipspace/project_zo.h

@@ -85,4 +85,27 @@ glm_project_zo(vec3 pos, mat4 m, vec4 vp, vec3 dest) {
   dest[1] = pos4[1] * vp[3] + vp[1];
 }
 
+/*!
+ * @brief map object's z coordinate to window coordinates
+ *
+ * Computing MVP:
+ *   glm_mat4_mul(proj, view, viewProj);
+ *   glm_mat4_mul(viewProj, model, MVP);
+ *
+ * @param[in]  v  object coordinates
+ * @param[in]  m  MVP matrix
+ *
+ * @returns projected z coordinate
+ */
+CGLM_INLINE
+float
+glm_project_z_zo(vec3 v, mat4 m) {
+  float z, w;
+
+  z = m[0][2] * v[0] + m[1][2] * v[1] + m[2][2] * v[2] + m[3][2];
+  w = m[0][3] * v[0] + m[1][3] * v[1] + m[2][3] * v[2] + m[3][3];
+
+  return z / w;
+}
+
 #endif /* cglm_project_zo_h */

include/cglm/project.h

@@ -114,6 +114,28 @@ glm_project(vec3 pos, mat4 m, vec4 vp, vec3 dest) {
 #endif
 }
 
+/*!
+ * @brief map object's z coordinate to window coordinates
+ *
+ * Computing MVP:
+ *   glm_mat4_mul(proj, view, viewProj);
+ *   glm_mat4_mul(viewProj, model, MVP);
+ *
+ * @param[in]  v  object coordinates
+ * @param[in]  m  MVP matrix
+ *
+ * @returns projected z coordinate
+ */
+CGLM_INLINE
+float
+glm_project_z(vec3 v, mat4 m) {
+#if CGLM_CONFIG_CLIP_CONTROL & CGLM_CLIP_CONTROL_ZO_BIT
+  return glm_project_z_zo(v, m);
+#elif CGLM_CONFIG_CLIP_CONTROL & CGLM_CLIP_CONTROL_NO_BIT
+  return glm_project_z_no(v, m);
+#endif
+}
+
 /*!
  * @brief define a picking region
  *

include/cglm/struct/clipspace/project_no.h

@@ -43,6 +43,7 @@
  * @param[in]  pos          point/position in viewport coordinates
  * @param[in]  invMat   matrix (see brief)
  * @param[in]  vp            viewport as [x, y, width, height]
+ *
  * @returns unprojected coordinates
  */
 CGLM_INLINE
@@ -63,6 +64,7 @@ glms_unprojecti_no(vec3s pos, mat4s invMat, vec4s vp, vec3 dest) {
  * @param[in]  pos      object coordinates
  * @param[in]  m          MVP matrix
  * @param[in]  vp        viewport as [x, y, width, height]
+ *
  * @returns projected coordinates
  */
 CGLM_INLINE
@@ -73,4 +75,22 @@ glms_project_no(vec3s pos, mat4s m, vec4s vp, vec3s dest) {
   return dest;
 }
 
+/*!
+ * @brief map object's z coordinate to window coordinates
+ *
+ * Computing MVP:
+ *   glm_mat4_mul(proj, view, viewProj);
+ *   glm_mat4_mul(viewProj, model, MVP);
+ *
+ * @param[in]  v object coordinates
+ * @param[in]  m MVP matrix
+ *
+ * @returns projected z coordinate
+ */
+CGLM_INLINE
+vec3s
+glms_project_z_no(vec3s v, mat4s m) {
+  return glm_project_z_no(v.raw, m.raw);
+}
+
 #endif /* cglms_project_rh_no_h */

include/cglm/struct/clipspace/project_zo.h

@@ -43,6 +43,7 @@
  * @param[in]  pos          point/position in viewport coordinates
  * @param[in]  invMat   matrix (see brief)
  * @param[in]  vp            viewport as [x, y, width, height]
+ *
  * @returns unprojected coordinates
  */
 CGLM_INLINE
@@ -63,6 +64,7 @@ glms_unprojecti_zo(vec3s pos, mat4s invMat, vec4s vp, vec3 dest) {
  * @param[in]  pos      object coordinates
  * @param[in]  m          MVP matrix
  * @param[in]  vp        viewport as [x, y, width, height]
+ *
  * @returns projected coordinates
  */
 CGLM_INLINE
@@ -73,4 +75,22 @@ glms_project_zo(vec3s pos, mat4s m, vec4s vp, vec3 dest) {
   return dest;
 }
 
+/*!
+ * @brief map object's z coordinate to window coordinates
+ *
+ * Computing MVP:
+ *   glm_mat4_mul(proj, view, viewProj);
+ *   glm_mat4_mul(viewProj, model, MVP);
+ *
+ * @param[in]  v object coordinates
+ * @param[in]  m MVP matrix
+ *
+ * @returns projected z coordinate
+ */
+CGLM_INLINE
+vec3s
+glms_project_z_zo(vec3s v, mat4s m) {
+  return glm_project_z_zo(v.raw, m.raw);
+}
+
 #endif /* cglm_project_zo_h */

src/project.c

@@ -26,6 +26,12 @@ glmc_project(vec3 pos, mat4 m, vec4 vp, vec3 dest) {
   glm_project(pos, m, vp, dest);
 }
 
+CGLM_EXPORT
+float
+glmc_project_z(vec3 pos, mat4 m) {
+  return glm_project_z(pos, m);
+}
+
 CGLM_EXPORT
 void
 glmc_pickmatrix(vec2 center, vec2 size, vec4 vp, mat4 dest) {