Add a premultiplied alpha render mode.

To render explosions with it, add a connector:
CONNECTORS 1
	0 3 0

Fixes ticket:3024.

lib/ivis_opengl/piedraw.cpp

@@ -142,11 +142,11 @@ static void pie_Draw3DShape2(iIMDShape *shape, int frame, PIELIGHT colour, PIELI
 	bool light = true;
 	bool shaders = pie_GetShaderAvailability();
 
-	pie_SetAlphaTest(true);
+	pie_SetAlphaTest((pieFlag & pie_PREMULTIPLIED) == 0);
 
 	/* Set fog status */
 	if (!(pieFlag & pie_FORCE_FOG) && 
-		(pieFlag & pie_ADDITIVE || pieFlag & pie_TRANSLUCENT || pieFlag & pie_BUTTON))
+		(pieFlag & pie_ADDITIVE || pieFlag & pie_TRANSLUCENT || pieFlag & pie_BUTTON || pieFlag & pie_PREMULTIPLIED))
 	{
 		pie_SetFogStatus(false);
 	}
@@ -168,6 +168,11 @@ static void pie_Draw3DShape2(iIMDShape *shape, int frame, PIELIGHT colour, PIELI
 		colour.byte.a = (UBYTE)pieFlagData;
 		light = false;
 	}
+	else if (pieFlag & pie_PREMULTIPLIED)
+	{
+		pie_SetRendMode(REND_PREMULTIPLIED);
+		light = false;
+	}
 	else
 	{
 		if (pieFlag & pie_BUTTON)
@@ -471,7 +476,7 @@ void pie_Draw3DShape(iIMDShape *shape, int frame, int team, PIELIGHT colour, int
 	}
 	else
 	{
-		if (pieFlag & (pie_ADDITIVE | pie_TRANSLUCENT) && !(pieFlag & pie_FORCE_IMMEDIATE))
+		if (pieFlag & (pie_ADDITIVE | pie_TRANSLUCENT | pie_PREMULTIPLIED) && !(pieFlag & pie_FORCE_IMMEDIATE))
 		{
 			if (tshapes_size <= nb_tshapes)
 			{

lib/ivis_opengl/piestate.cpp

@@ -636,6 +636,11 @@ void pie_SetRendMode(REND_MODE rendMode)
 				glBlendFunc(GL_ZERO, GL_SRC_COLOR);
 				break;
 
+			case REND_PREMULTIPLIED:
+				glEnable(GL_BLEND);
+				glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
+				break;
+
 			default:
 				ASSERT(false, "Bad render state");
 				break;

lib/ivis_opengl/pietypes.h

@@ -56,6 +56,7 @@
 #define pie_BUTTON              0x40
 #define pie_SHADOW              0x80
 #define pie_STATIC_SHADOW       0x100
+#define pie_PREMULTIPLIED       0x200
 #define pie_FORCE_IMMEDIATE     0x400
 
 #define pie_RAISE_SCALE			256
@@ -74,7 +75,8 @@ enum REND_MODE
 	REND_ALPHA,
 	REND_ADDITIVE,
 	REND_OPAQUE,
-	REND_MULTIPLICATIVE
+	REND_MULTIPLICATIVE,
+	REND_PREMULTIPLIED,
 };
 
 enum DEPTH_MODE

src/display3d.cpp

@@ -1279,6 +1279,7 @@ void	renderProjectile(PROJECTILE *psCurr)
 	{
 		bool rollToCamera = false;
 		bool pitchToCamera = false;
+		bool premultiplied = false;
 		bool additive = psStats->weaponSubClass == WSC_ROCKET || psStats->weaponSubClass == WSC_MISSILE || psStats->weaponSubClass == WSC_SLOWROCKET || psStats->weaponSubClass == WSC_SLOWMISSILE;
 
 		if (pIMD->nconnectors >= 2)
@@ -1292,6 +1293,7 @@ void	renderProjectile(PROJECTILE *psCurr)
 			{
 				case 1: additive = false; break;
 				case 2: additive = true; break;
+				case 3: additive = false; premultiplied = true; break;
 			}
 		}
 
@@ -1349,7 +1351,11 @@ void	renderProjectile(PROJECTILE *psCurr)
 			camera -= Vector3i(-pIMD->connectors[1].x, -pIMD->connectors[1].y, -pIMD->connectors[1].z);
 		}
 
-		if (additive)
+		if (premultiplied)
+		{
+			pie_Draw3DShape(pIMD, 0, 0, WZCOL_WHITE, pie_PREMULTIPLIED, 0);
+		}
+		else if (additive)
 		{
 			pie_Draw3DShape(pIMD, 0, 0, WZCOL_WHITE, pie_ADDITIVE, 164);
 		}

src/effects.cpp

@@ -1745,7 +1745,20 @@ static void renderExplosionEffect(const EFFECT *psEffect)
 		pie_MatScale(psEffect->size / 100.f);
 	}
 
-	if(psEffect->type == EXPLOSION_TYPE_PLASMA)
+	bool premultiplied = false;
+	if (psEffect->imd->nconnectors >= 1)
+	{
+		switch (psEffect->imd->connectors[0].y)
+		{
+			case 3: premultiplied = true; break;
+		}
+	}
+
+	if (premultiplied)
+	{
+		pie_Draw3DShape(psEffect->imd, psEffect->frameNumber, 0, brightness, pie_PREMULTIPLIED, 0);
+	}
+	else if (psEffect->type == EXPLOSION_TYPE_PLASMA)
 	{
 		pie_Draw3DShape(psEffect->imd, psEffect->frameNumber, 0, brightness, pie_ADDITIVE, EFFECT_PLASMA_ADDITIVE);
 	}