OPENGL: Fix OpenGL ES v1 builds without GLAD

backends/graphics/opengl/context.cpp

@@ -204,8 +204,10 @@ void OpenGLGraphicsManager::initializeGLContext() {
 	}
 
 	// Log features supported by GL context.
+#if !USE_FORCED_GLES
 	if (g_context.shadersSupported)
 		debug(5, "GLSL version: %s", glGetString(GL_SHADING_LANGUAGE_VERSION));
+#endif
 	debug(5, "OpenGL vendor: %s", glGetString(GL_VENDOR));
 	debug(5, "OpenGL renderer: %s", glGetString(GL_RENDERER));
 	debug(5, "OpenGL: NPOT texture support: %d", g_context.NPOTSupported);

configure

@@ -5400,8 +5400,9 @@ if test "$_opengl_glad" = "no" -a "$_opengl_mode" != "none"; then
 	# 1) GL/gl.h         This is usually used on POSIX and Windows systems
 	# 2) OpenGL/gl.h     This is used on macOS
 	# 3) GLES2/gl2.h     This is used for OpenGL ES 2.x
+	# 3) GLES/gl.h       This is used for OpenGL ES 1.x
 	_opengl_can_compile=no
-	for i in "GL/gl.h" "OpenGL/gl.h" "GLES2/gl2.h"; do
+	for i in "GL/gl.h" "OpenGL/gl.h" "GLES2/gl2.h" "GLES/gl.h"; do
 		# Test the current header for OpenGL
 		if test "$_opengl_mode" = "gl" -o "$_opengl_mode" = "any" ; then
 			cat > $TMPC << EOF
@@ -5449,6 +5450,11 @@ EOF
 					break
 				fi
 			done
+		elif test "$_opengl_mode" = "gles" ; then
+			OPENGL_LIBS="-lGLESv1_CM"
+			if cc_check_no_clean $DEFINES $OPENGL_CFLAGS $OPENGL_LIBS; then
+				_opengl_can_compile=yes
+			fi
 		else
 			case $_host_os in
 			darwin*)

graphics/opengl/system_headers.h

@@ -84,6 +84,18 @@
 		#define GL_MAX_SAMPLES 0x8D57
 	#endif
 
+#elif USE_FORCED_GLES
+
+	#define GL_GLEXT_PROTOTYPES
+	#if defined(IPHONE)
+		#include <OpenGLES/ES1/gl.h>
+		#include <OpenGLES/ES1/glext.h>
+	#else
+		#include <GLES/gl.h>
+		#include <GLES/glext.h>
+	#endif
+	#undef GL_GLEXT_PROTOTYPES
+
 #endif
 #endif