gles2gsg: Support gl-depth-zero-to-one in OpenGL ES 2+

Requires GL_EXT_clip_control support in the driver.

panda/src/gles2gsg/gles2gsg.h

@@ -120,6 +120,8 @@ typedef char GLchar;
 #define GL_ONE_MINUS_SRC1_COLOR GL_ONE_MINUS_SRC1_COLOR_EXT
 #define GL_SRC1_ALPHA GL_SRC1_ALPHA_EXT
 #define GL_ONE_MINUS_SRC1_ALPHA GL_ONE_MINUS_SRC1_ALPHA_EXT
+#define GL_LOWER_LEFT GL_LOWER_LEFT_EXT
+#define GL_ZERO_TO_ONE GL_ZERO_TO_ONE_EXT
 
 #define GL_DEBUG_OUTPUT_SYNCHRONOUS GL_DEBUG_OUTPUT_SYNCHRONOUS_KHR
 #define GL_DEBUG_TYPE_PERFORMANCE GL_DEBUG_TYPE_PERFORMANCE_KHR

panda/src/gles2gsg/panda_esgl2ext.h

@@ -1050,6 +1050,20 @@ GL_APICALL void GL_APIENTRY glBufferStorageEXT (GLenum target, GLsizeiptr size,
 #endif
 #endif /* GL_EXT_buffer_storage */
 
+#ifndef GL_EXT_clip_control
+#define GL_EXT_clip_control 1
+#define GL_LOWER_LEFT_EXT                 0x8CA1
+#define GL_UPPER_LEFT_EXT                 0x8CA2
+#define GL_NEGATIVE_ONE_TO_ONE_EXT        0x935E
+#define GL_ZERO_TO_ONE_EXT                0x935F
+#define GL_CLIP_ORIGIN_EXT                0x935C
+#define GL_CLIP_DEPTH_MODE_EXT            0x935D
+typedef void (GL_APIENTRYP PFNGLCLIPCONTROLEXTPROC) (GLenum origin, GLenum depth);
+#ifdef GL_GLEXT_PROTOTYPES
+GL_APICALL void GL_APIENTRY glClipControlEXT (GLenum origin, GLenum depth);
+#endif
+#endif /* GL_EXT_clip_control */
+
 #ifndef GL_EXT_color_buffer_float
 #define GL_EXT_color_buffer_float 1
 #endif /* GL_EXT_color_buffer_float */

panda/src/glstuff/glGraphicsStateGuardian_src.cxx

@@ -3293,23 +3293,30 @@ reset() {
 #endif
 
   // Set depth range from zero to one if requested.
-#ifndef OPENGLES
+#ifndef OPENGLES_1
   _use_depth_zero_to_one = false;
   _use_remapped_depth_range = false;
 
   if (gl_depth_zero_to_one) {
+#ifndef OPENGLES
+    PFNGLCLIPCONTROLPROC pglClipControl = nullptr;
     if (is_at_least_gl_version(4, 5) || has_extension("GL_ARB_clip_control")) {
-      PFNGLCLIPCONTROLPROC pglClipControl =
-        (PFNGLCLIPCONTROLPROC)get_extension_func("glClipControl");
+      pglClipControl = (PFNGLCLIPCONTROLPROC)get_extension_func("glClipControl");
+    }
+#else
+    PFNGLCLIPCONTROLEXTPROC pglClipControl = nullptr;
+    if (has_extension("GL_EXT_clip_control")) {
+      pglClipControl = (PFNGLCLIPCONTROLEXTPROC)get_extension_func("glClipControlEXT");
+    }
+#endif
 
-      if (pglClipControl != nullptr) {
-        pglClipControl(GL_LOWER_LEFT, GL_ZERO_TO_ONE);
-        _use_depth_zero_to_one = true;
+    if (pglClipControl != nullptr) {
+      pglClipControl(GL_LOWER_LEFT, GL_ZERO_TO_ONE);
+      _use_depth_zero_to_one = true;
 
-        if (GLCAT.is_debug()) {
-          GLCAT.debug()
-            << "Set zero-to-one depth using glClipControl\n";
-        }
+      if (GLCAT.is_debug()) {
+        GLCAT.debug()
+          << "Set zero-to-one depth using glClipControl\n";
       }
     }/* else if (has_extension("GL_NV_depth_buffer_float")) {
       // Alternatively, all GeForce 8+ and even some AMD drivers support this

panda/src/glstuff/glGraphicsStateGuardian_src.h

@@ -761,9 +761,11 @@ protected:
 #endif
 
 public:
-#ifndef OPENGLES
+#ifndef OPENGLES_1
   bool _use_depth_zero_to_one;
   bool _use_remapped_depth_range;
+#endif
+#ifndef OPENGLES
   PFNGLDEPTHRANGEDNVPROC _glDepthRangedNV;
 #endif