Additive and substractive picture support

[gadesx]

With RPG Maker XP & Vx ace there was an added to
show pictures additives and substractives.

In Rpg maker 2003 with dynrpg there's a plugin that support it:
https://rpgmaker.net/engines/rt2k3/utilities/11/

Actual comparison of a light in player using alpha channel (that looks like similar to the own rpg maker pictures with transparency) and additive light of blending plugin with dynrpg

[Ghabry]

Looks like thie Enhancement has unlikely conflicts with existing games (is file ending based, .xxx.png).

And is fast because is only required once on load. Related pixman ops:
OP_ADD, OP_SATURATE, OP_MULTIPLY

[Ghabry]

Can @gadesx explain why the pictures are displayed with 50% transparency and faded out in RPG_RT? EasyRPG starts with 100% transparency and the editor shows it the same way.

[Ghabry]

Looks DynRPG specific, doesn't happen when I replace the RPG_RT m(

[gadesx]

Added a image here with the light I used as example,
the plugin ignore the colours like black, adding only
brighter colours of below.

[fdelapena]

Last year @elsemieni tried to implement this feature but had some differences in behavior (layering, etc.) that could require diving deeper to match existing RPG_RT patches, however looks great to start with: ff64fd8

[Ghabry]

Maniac patch has also support for some of the blend modes

[Ghabry]

Fixed by #2628

Because this is powered by Pixman it also supports 32 bit PNGs with Alpha channel properly
(Contrary to Maniac Patch which only has limited alpha channel support)

[cremno]

Pixman doesn't support the (odd) subtract blend mode though.

[Ghabry]

yeah it only supports "Difference". Defined as abs(xB−xA), so the behaviour is different (wraparound)

[Ghabry]

Potential patch:

diff --git a/src/sprite.cpp b/src/sprite.cpp
index 16203e9fc..377c03819 100644
--- a/src/sprite.cpp
+++ b/src/sprite.cpp
@@ -114,11 +114,43 @@ BitmapRef Sprite::Refresh(Rect& rect) {
 }
 
 void Sprite::SetBitmap(BitmapRef const& nbitmap) {
+	if (nbitmap == bitmap) {
+		return;
+	}
+
 	bitmap = nbitmap;
 	if (!bitmap) {
 		src_rect = Rect();
 	} else {
 		src_rect = bitmap->GetRect();
+
+		// EasyRPG Extension: Set the Blend Mode based on the filename, e.g. ".add.png" for "Additive"
+		SetBlendType(0);
+		StringView filename = bitmap->GetFilename();
+		if (filename.size() >= 8 && filename[filename.size() - 4] == '.' && filename[filename.size() - 8] == '.') {
+			filename = filename.substr(filename.size() - 7, 3);
+			constexpr std::array<std::pair<StringView, Bitmap::BlendMode>, 13> exts = {{
+				{"add", Bitmap::BlendMode::Additive},
+				{"clb", Bitmap::BlendMode::ColorBurn},
+				{"cld", Bitmap::BlendMode::ColorDodge},
+				{"dif", Bitmap::BlendMode::Difference},
+				{"drk", Bitmap::BlendMode::Darken},
+				{"exc", Bitmap::BlendMode::Exclusion},
+				{"hlg", Bitmap::BlendMode::HardLight},
+				{"lgh", Bitmap::BlendMode::Lighten},
+				{"mul", Bitmap::BlendMode::Multiply},
+				{"ove", Bitmap::BlendMode::Overlay},
+				{"sat", Bitmap::BlendMode::Saturate},
+				{"slg", Bitmap::BlendMode::SoftLight},
+				{"xor", Bitmap::BlendMode::XOR}
+			}};
+			auto it = std::lower_bound(exts.begin(), exts.end(), filename, [](const auto& e, const auto& fname) {
+				return e.first < fname;
+			});
+			if (it != exts.end() && it->first == filename) {
+				SetBlendType((int)it->second);
+			}
+		}
 	}
 
 	src_rect_effect = src_rect;
diff --git a/src/sprite_picture.cpp b/src/sprite_picture.cpp
index 58f094132..8c005c371 100644
--- a/src/sprite_picture.cpp
+++ b/src/sprite_picture.cpp
@@ -144,7 +144,9 @@ void Sprite_Picture::Draw(Bitmap& dst) {
 
 	SetFlipX(data.easyrpg_flip_horizontal);
 	SetFlipY(data.easyrpg_flip_vertical);
-	SetBlendType(data.easyrpg_blend_mode);
+	if (static_cast<Bitmap::BlendMode>(data.easyrpg_blend_mode) != Bitmap::BlendMode::Default) {
+		SetBlendType(data.easyrpg_blend_mode);
+	}
 
 	Sprite::Draw(dst);
 }
--