GL: recognize and implement EXT_depth_clamp on GLES.

Makes Renderer::Feature::DepthClamp available not just on desktop GL
anymore.

doc/changelog.dox

@@ -492,6 +492,8 @@ See also:
     complement @relativeref{GL::Framebuffer::InvalidationAttachment,Depth} and
     @relativeref{GL::Framebuffer::InvalidationAttachment,Stencil} (see
     [mosra/magnum#554](https://github.com/mosra/magnum/pull/554))
+-   @ref GL::Renderer::Feature::DepthClamp is now exposed on OpenGL ES as well,
+    using the @gl_extension{EXT,depth_clamp} extension
 -   Added @ref GL::Shader::wrap() and @relativeref{GL::Shader,release()}
 -   New @ref MAGNUM_GL_ABSTRACTSHADERPROGRAM_SUBCLASS_DRAW_IMPLEMENTATION() and
     @ref MAGNUM_GL_ABSTRACTSHADERPROGRAM_SUBCLASS_DISPATCH_IMPLEMENTATION()

doc/opengl-support.dox

@@ -482,6 +482,7 @@ Extension                                   | Status
 @gl_extension{EXT,texture_compression_rgtc} | done
 @gl_extension{EXT,texture_compression_bptc} | done
 @gl_extension{EXT,texture_compression_s3tc_srgb} | done
+@gl_extension{EXT,depth_clamp}              | done
 @gl_extension{IMG,texture_compression_pvrtc} | done
 @gl_extension2{KHR,texture_compression_astc_hdr,KHR_texture_compression_astc_hdr} | done
 @gl_extension2{KHR,blend_equation_advanced_coherent,KHR_blend_equation_advanced} | done

src/Magnum/GL/Context.cpp

@@ -361,6 +361,7 @@ constexpr Extension ExtensionList[]{
     #endif
     Extensions::EXT::debug_label{},
     Extensions::EXT::debug_marker{},
+    Extensions::EXT::depth_clamp{},
     Extensions::EXT::disjoint_timer_query{},
     Extensions::EXT::draw_elements_base_vertex{},
     Extensions::EXT::multi_draw_arrays{},

src/Magnum/GL/Extensions.h

@@ -479,8 +479,9 @@ namespace ANDROID {
     _extension( 70,EXT,texture_compression_bptc,    GLES300,    None) // #287
     #endif
     _extension( 71,EXT,texture_compression_s3tc_srgb, GLES200,  None) // #289
+    _extension( 72,EXT,depth_clamp,                 GLES200,    None) // #309
 } namespace IMG {
-    _extension( 72,IMG,texture_compression_pvrtc,   GLES200,    None) // #54
+    _extension( 73,IMG,texture_compression_pvrtc,   GLES200,    None) // #54
 } namespace KHR {
     _extension( 80,KHR,texture_compression_astc_ldr,GLES200, GLES320) // #117
     _extension( 81,KHR,texture_compression_astc_hdr,GLES200,    None) // #117

src/Magnum/GL/Renderer.h

@@ -324,14 +324,18 @@ class MAGNUM_GL_EXPORT Renderer {
             #endif
             #endif
 
-            #ifndef MAGNUM_TARGET_GLES
+            #ifndef MAGNUM_TARGET_WEBGL
             /**
              * Depth clamping. If enabled, ignores near and far clipping plane.
              * @requires_gl32 Extension @gl_extension{ARB,depth_clamp}
-             * @requires_gl Depth clamping is not available in OpenGL ES and
+             * @requires_es_extension Extension @gl_extension{EXT,depth_clamp}
-             *      WebGL.
+             * @requires_gles Depth clamping is not available in WebGL.
              */
+            #ifndef MAGNUM_TARGET_GLES
             DepthClamp = GL_DEPTH_CLAMP,
+            #else
+            DepthClamp = GL_DEPTH_CLAMP_EXT,
+            #endif
             #endif
 
             /**

src/MagnumExternal/OpenGL/GLES2/extensions.txt

@@ -93,6 +93,7 @@ extension EXT_pvrtc_sRGB                        optional
 extension EXT_draw_elements_base_vertex         optional
 extension EXT_polygon_offset_clamp              optional
 extension EXT_texture_compression_s3tc_srgb     optional
+extension EXT_depth_clamp                       optional
 extension IMG_texture_compression_pvrtc         optional
 # extension KHR_texture_compression_astc_hdr    optional
 extension KHR_blend_equation_advanced_coherent  optional

src/MagnumExternal/OpenGL/GLES2/flextGL.h

@@ -1004,6 +1004,10 @@ typedef void (APIENTRY *GLDEBUGPROCKHR)(GLenum source,GLenum type,GLuint id,GLen
 #define GL_COMPRESSED_SRGB_ALPHA_S3TC_DXT3_EXT 0x8C4E
 #define GL_COMPRESSED_SRGB_ALPHA_S3TC_DXT5_EXT 0x8C4F
 
+/* GL_EXT_depth_clamp */
+
+#define GL_DEPTH_CLAMP_EXT 0x864F
+
 /* GL_IMG_texture_compression_pvrtc */
 
 #define GL_COMPRESSED_RGB_PVRTC_4BPPV1_IMG 0x8C00

src/MagnumExternal/OpenGL/GLES2/flextGLWindowsDesktop.h

@@ -1000,6 +1000,10 @@ typedef void (APIENTRY *GLDEBUGPROCKHR)(GLenum source,GLenum type,GLuint id,GLen
 #define GL_COMPRESSED_SRGB_ALPHA_S3TC_DXT3_EXT 0x8C4E
 #define GL_COMPRESSED_SRGB_ALPHA_S3TC_DXT5_EXT 0x8C4F
 
+/* GL_EXT_depth_clamp */
+
+#define GL_DEPTH_CLAMP_EXT 0x864F
+
 /* GL_IMG_texture_compression_pvrtc */
 
 #define GL_COMPRESSED_RGB_PVRTC_4BPPV1_IMG 0x8C00

src/MagnumExternal/OpenGL/GLES3/extensions.txt

@@ -69,6 +69,7 @@ extension EXT_clip_cull_distance                    optional
 extension EXT_texture_compression_rgtc              optional
 extension EXT_texture_compression_bptc              optional
 extension EXT_texture_compression_s3tc_srgb         optional
+extension EXT_depth_clamp                           optional
 extension IMG_texture_compression_pvrtc             optional
 # extension KHR_texture_compression_astc_hdr        optional
 extension KHR_blend_equation_advanced_coherent      optional

src/MagnumExternal/OpenGL/GLES3/flextGL.h

@@ -1629,6 +1629,10 @@ typedef void (APIENTRY *GLDEBUGPROCKHR)(GLenum source,GLenum type,GLuint id,GLen
 #define GL_COMPRESSED_SRGB_ALPHA_S3TC_DXT3_EXT 0x8C4E
 #define GL_COMPRESSED_SRGB_ALPHA_S3TC_DXT5_EXT 0x8C4F
 
+/* GL_EXT_depth_clamp */
+
+#define GL_DEPTH_CLAMP_EXT 0x864F
+
 /* GL_IMG_texture_compression_pvrtc */
 
 #define GL_COMPRESSED_RGB_PVRTC_4BPPV1_IMG 0x8C00

src/MagnumExternal/OpenGL/GLES3/flextGLWindowsDesktop.h

@@ -1622,6 +1622,10 @@ typedef void (APIENTRY *GLDEBUGPROCKHR)(GLenum source,GLenum type,GLuint id,GLen
 #define GL_COMPRESSED_SRGB_ALPHA_S3TC_DXT3_EXT 0x8C4E
 #define GL_COMPRESSED_SRGB_ALPHA_S3TC_DXT5_EXT 0x8C4F
 
+/* GL_EXT_depth_clamp */
+
+#define GL_DEPTH_CLAMP_EXT 0x864F
+
 /* GL_IMG_texture_compression_pvrtc */
 
 #define GL_COMPRESSED_RGB_PVRTC_4BPPV1_IMG 0x8C00