GRAPHICS: Fix transparency blending

Depth writing needs to be disabled for transparent materials.

The material now has a transparency hint member, ideally
read from the model. If the model does not provide a hint
the transparency is inferred from the textures and diffuse
color. Since Aurora textures compressed with DXT1 are always
opaque, we override the default Ogre claim that DXT1 textures
have an alpha channel.

src/graphics/aurora/model_nwn.cpp

@@ -522,8 +522,8 @@ void Model_NWN::readBinaryMesh(ParserContext &ctx) {
 	if (!render)
 		ctx.nodeEntity->dontRender = true;
 
-	bool transparencyHint;
-	transparencyHint = ctx.mdl->readUint32LE() == 1;
+	bool transparencyHint = ctx.mdl->readUint32LE() == 1;
+	ctx.material.transparency = transparencyHint ? kTransparencyHintTransparent : kTransparencyHintOpaque;
 
 	ctx.mdl->skip(4); // Unknown
 
@@ -978,6 +978,8 @@ void Model_NWN::loadASCIINode(ParserContext &ctx, Ogre::SceneNode *parent,
 		} else if (line[0] == "transparencyhint") {
 			bool transparencyHint;
 			line[1].parse(transparencyHint);
+
+			ctx.material.transparency = transparencyHint ? kTransparencyHintTransparent : kTransparencyHintOpaque;
 		} else if (line[0] == "danglymesh") {
 			line[1].parse(dangly);
 		} else if (line[0] == "constraints") {

src/graphics/materialman.cpp

@@ -61,6 +61,8 @@ void MaterialDeclaration::reset() {
 	writeColor     = true;
 	writeDepth     = true;
 
+	transparency = kTransparencyHintUnknown;
+
 	textures.clear();
 }
 
@@ -157,16 +159,33 @@ void MaterialManager::create(const MaterialDeclaration &decl, Ogre::MaterialPtr
 			texState->setTexture(texture);
 			texState->setTextureAddressingMode(Ogre::TextureUnitState::TAM_WRAP);
 
-			if (!texture->hasAlpha())
+			// DXT1 textures used in Aurora games are always opaque
+			if (!texture->hasAlpha() || ((PixelFormat)texture->getFormat() == kPixelFormatDXT1))
 				transparent = false;
 
 		} else
 			texState->setBlank();
 	}
 
-	material->getTechnique(0)->getPass(0)->setSceneBlending(transparent ? Ogre::SBT_TRANSPARENT_ALPHA : Ogre::SBT_REPLACE);
+	// Even if the textures themselves aren't tranparent, the color might still be
+	if (decl.diffuse[3] != 1.0)
+		transparent = true;
+
+	// Figure out whether this material is transparent.
+	// If we don't get a hint from the declaration, try to infer
+	// it from the texture and color information gathered above.
+	TransparencyHint transparency = decl.transparency;
+	if (transparency == kTransparencyHintUnknown)
+		transparency = transparent ? kTransparencyHintTransparent : kTransparencyHintOpaque;
+
+	if (transparency == kTransparencyHintTransparent) {
+		material->getTechnique(0)->getPass(0)->setSceneBlending(Ogre::SBT_TRANSPARENT_ALPHA);
+		material->getTechnique(0)->getPass(0)->setDepthWriteEnabled(false);
+	} else {
+		material->getTechnique(0)->getPass(0)->setSceneBlending(Ogre::SBT_REPLACE);
+		material->getTechnique(0)->getPass(0)->setDepthWriteEnabled(decl.writeDepth);
+	}
 
-	material->getTechnique(0)->getPass(0)->setDepthWriteEnabled(decl.writeDepth);
 	material->getTechnique(0)->getPass(0)->setColourWriteEnabled(decl.writeColor);
 
 	material->setReceiveShadows(decl.receiveShadows);

src/graphics/materialman.h

@@ -36,6 +36,8 @@
 #include "common/singleton.h"
 #include "common/ustring.h"
 
+#include "graphics/types.h"
+
 namespace Graphics {
 
 struct MaterialDeclaration {
@@ -53,6 +55,8 @@ struct MaterialDeclaration {
 	bool writeColor;
 	bool writeDepth;
 
+	TransparencyHint transparency;
+
 	MaterialDeclaration();
 
 	void reset();

src/graphics/types.h

@@ -36,6 +36,13 @@
 
 namespace Graphics {
 
+/** Hinting at a materials transparency. */
+enum TransparencyHint {
+	kTransparencyHintOpaque      = 0, ///< This material is opaque.
+	kTransparencyHintTransparent = 1, ///< This material is transparent.
+	kTransparencyHintUnknown     = 2  ///< Unknown whether the material is transparent.
+};
+
 enum PixelFormat {
 	kPixelFormatNone = Ogre::PF_UNKNOWN,