Allow texel buffers in OpenGL ES, when supported by the system.

src/modules/graphics/Shader.cpp

@@ -78,6 +78,11 @@ static const char global_syntax[] = R"(
 #ifdef GL_OES_standard_derivatives
 #extension GL_OES_standard_derivatives : enable
 #endif
+#if __VERSION__ >= 300 && defined(GL_OES_texture_buffer)
+#extension GL_OES_texture_buffer : enable
+#elif __VERSION__ >= 300 && defined(GL_EXT_texture_buffer)
+#extension GL_EXT_texture_buffer : enable
+#endif
 )";
 
 static const char render_uniforms[] = R"(

src/modules/graphics/opengl/Buffer.cpp

@@ -151,7 +151,14 @@ bool Buffer::load(const void *initialdata)
 		glGenTextures(1, &texture);
 		gl.bindBufferTextureToUnit(texture, 0, false, true);
 
-		glTexBuffer(target, getGLFormat(getDataMember(0).decl.format), buffer);
+		GLenum glformat = getGLFormat(getDataMember(0).decl.format);
+
+		if (GLAD_VERSION_3_1)
+			glTexBuffer(target, glformat, buffer);
+		else if (GLAD_OES_texture_buffer)
+			glTexBufferOES(target, glformat, buffer);
+		else if (GLAD_EXT_texture_buffer)
+			glTexBufferEXT(target, glformat, buffer);
 	}
 
 	return (glGetError() == GL_NO_ERROR);

src/modules/graphics/opengl/OpenGL.cpp

@@ -1479,8 +1479,8 @@ bool OpenGL::isBufferUsageSupported(BufferUsage usage) const
 	case BUFFERUSAGE_INDEX:
 		return true;
 	case BUFFERUSAGE_TEXEL:
-		// Not supported in ES until 3.2, which we don't support shaders for...
-		return GLAD_VERSION_3_1;
+		// Not supported in ES until 3.2, so we rely on extensions there...
+		return GLAD_VERSION_3_1 || GLAD_OES_texture_buffer || GLAD_EXT_texture_buffer;
 	case BUFFERUSAGE_SHADER_STORAGE:
 		return (GLAD_VERSION_4_3 && isCoreProfile()) || GLAD_ES_VERSION_3_1;
 	case BUFFERUSAGE_MAX_ENUM: