ES 3: Use sized internal formats for half float textures (#1015)

Co-authored-by: Alex Cristici <alex.cristici@gmail.com>
Co-authored-by: Bart Louwers <bart@emeel.net>

src/mbgl/gl/context.cpp

@@ -218,7 +218,7 @@ std::unique_ptr<gfx::TextureResource> Context::createTextureResource(
     texture[0] = static_cast<gl::TextureResource&>(*resource).texture;
 
     // Creates an empty texture with the specified size and format.
-    MBGL_CHECK_ERROR(glTexImage2D(GL_TEXTURE_2D, 0, Enum<gfx::TexturePixelType>::to(format),
+    MBGL_CHECK_ERROR(glTexImage2D(GL_TEXTURE_2D, 0, Enum<gfx::TexturePixelType>::sizedFor(format, type),
                                   size.width, size.height, 0,
                                   Enum<gfx::TexturePixelType>::to(format),
                                   Enum<gfx::TextureChannelDataType>::to(type), nullptr));

src/mbgl/gl/enum.cpp

@@ -265,6 +265,26 @@ platform::GLenum Enum<gfx::TexturePixelType>::to(const gfx::TexturePixelType val
     return GL_INVALID_ENUM;
 }
 
+template <> template<>
+platform::GLenum Enum<gfx::TexturePixelType>::sizedFor<>(const gfx::TexturePixelType value,
+    gfx::TextureChannelDataType type)
+{
+    switch (type) {
+        case gfx::TextureChannelDataType::UnsignedByte: {
+            return Enum<gfx::TexturePixelType>::to(value);
+        }
+        case gfx::TextureChannelDataType::HalfFloat: {
+            switch (value) {
+                case gfx::TexturePixelType::RGBA:
+                    return GL_RGBA16F;
+                default: break;
+            }
+        }
+    }
+
+    return GL_INVALID_ENUM;
+}
+
 template <>
 gfx::TextureChannelDataType Enum<gfx::TextureChannelDataType>::from(const platform::GLint value) {
     switch (value) {

src/mbgl/gl/enum.hpp

@@ -15,6 +15,9 @@ public:
 
     static T from(InType);
     static OutType to(T);
+
+    template<typename U>
+    static OutType sizedFor(T, U type);
 };
 
 } // namespace gl