Allow theming of powerup/attachment icons (#4258)

* Allow theming of powerup/attachment icons
Icons were optimized with `pngquant` then `optimize_data.sh`

* Change help screens to use icons from icons folder rather than `models`

data/gui/screens/help3.stkgui

@@ -32,57 +32,57 @@
                 <spacer height="2%" width="10"/>
 
                 <div width="100%" proportion="1" layout="horizontal-row">
-                    <icon align="center" width="8%" height="100%" icon="gui/icons/bubblegum_icon.png" alt_icon="models/bubblegum-icon.png"/>
+                    <icon align="center" width="8%" height="100%" icon="gui/icons/bubblegum-icon.png"/>
                     <spacer width="3%" height="100%"/>
                     <bubble proportion="1" height="100%" text="BubbleGum - protect yourself with a shield, or use while looking back to leave a sticky pink puddle behind you."/>
                 </div>
 
                 <div width="100%" proportion="1" layout="horizontal-row">
-                     <icon align="center" width="8%" height="100%" icon="gui/icons/zipper_collect.png" alt_icon="models/zipper_collect.png"/>
+                     <icon align="center" width="8%" height="100%" icon="gui/icons/zipper_collect.png"/>
                      <spacer width="3%" height="100%"/>
                      <bubble proportion="1" height="100%" text="Zipper - will give you a strong speed boost. But beware of not losing control of your kart!"/>
                 </div>
 
                 <div width="100%" proportion="1" layout="horizontal-row">
-                    <icon align="center" width="8%" height="100%" icon="gui/icons/cake_icon.png" alt_icon="models/cake-icon.png"/>
+                    <icon align="center" width="8%" height="100%" icon="gui/icons/cake-icon.png"/>
                     <spacer width="3%" height="100%"/>
                     <bubble proportion="1" height="100%"
                             text="Cake - thrown at the closest rival, best on short ranges and long straights. It also affects other karts close to the explosion."/>
                 </div>
 
                 <div width="100%" proportion="1" layout="horizontal-row">
-                    <icon align="center" width="8%" height="100%" icon="gui/icons/plunger_icon.png" alt_icon="models/plunger-icon.png"/>
+                    <icon align="center" width="8%" height="100%" icon="gui/icons/plunger-icon.png"/>
                     <spacer width="3%" height="100%"/>
                     <bubble proportion="1" height="100%" text="Plunger - throw straight to pull an opponent back, or throw while looking back to make one lose sight."/>
                 </div>
 
                 <div width="100%" proportion="1" layout="horizontal-row">
-                    <icon align="center" width="8%" height="100%" icon="gui/icons/bowling_icon.png" alt_icon="models/bowling-icon.png"/>
+                    <icon align="center" width="8%" height="100%" icon="gui/icons/bowling-icon.png"/>
                     <spacer width="3%" height="100%"/>
                     <bubble proportion="1" height="100%"
                             text="Bowling Ball - goes straight until it strikes, it can bounce off walls. If you are looking back, it will be thrown backwards."/>
                 </div>
 
                 <div width="100%" proportion="1" layout="horizontal-row">
-                    <icon align="center" width="8%" height="100%" icon="gui/icons/parachute_icon.png" alt_icon="models/parachute-icon.png"/>
+                    <icon align="center" width="8%" height="100%" icon="gui/icons/parachute-icon.png"/>
                     <spacer width="3%" height="100%"/>
                     <bubble proportion="1" height="100%" text="Parachute - slows down all karts in a better position."/>
                 </div>
 
                 <div width="100%" proportion="1" layout="horizontal-row">
-                    <icon align="center" width="8%" height="100%" icon="gui/icons/swap_icon.png" alt_icon="models/swap-icon.png"/>
+                    <icon align="center" width="8%" height="100%" icon="gui/icons/swap-icon.png"/>
                     <spacer width="3%" height="100%"/>
                     <bubble proportion="1" height="100%" text="Swapper - gift boxes are transformed into bananas, nitro cans into bubblegums, and vice versa for a short time."/>
                 </div>
 
                 <div width="100%" proportion="1" layout="horizontal-row">
-                     <icon align="center" width="8%" height="100%" icon="gui/icons/rubber_ball_icon.png" alt_icon="models/rubber_ball-icon.png"/>
+                     <icon align="center" width="8%" height="100%" icon="gui/icons/rubber_ball-icon.png"/>
                      <spacer width="3%" height="100%"/>
                      <bubble proportion="1" height="100%" text="Basket Ball - bounces after the leader, and might squash and slow down karts down on the way."/>
                 </div>
 
                 <div width="100%" proportion="1" layout="horizontal-row">
-                     <icon align="center" width="8%" height="100%" icon="gui/icons/swatter_icon.png" alt_icon="models/swatter-icon.png"/>
+                     <icon align="center" width="8%" height="100%" icon="gui/icons/swatter-icon.png"/>
                      <spacer width="3%" height="100%"/>
                      <bubble proportion="1" height="100%" text="Swatter - will squash karts close by, slowing them down. Can also be used to remove parachutes and bombs."/>
                 </div>

data/gui/screens/help4.stkgui

@@ -32,7 +32,7 @@
                 <spacer height="2%" width="10"/>                
 
                 <div width="100%" proportion="2" layout="horizontal-row">
-                    <icon align="center" width="8%" height="100%" icon="gui/icons/anchor_icon.png" alt_icon="models/anchor-icon.png"/>
+                    <icon align="center" width="8%" height="100%" icon="gui/icons/anchor-icon.png"/>
                     <spacer width="3%" height="100%"/>
                     <bubble proportion="1" height="100%"
                             I18N="In the help menu"
@@ -40,7 +40,7 @@
                 </div>
                 
                 <div width="100%" proportion="2" layout="horizontal-row">
-                    <icon align="center" width="8%" height="100%" icon="gui/icons/parachute_icon.png" alt_icon="models/parachute-icon.png"/>
+                    <icon align="center" width="8%" height="100%" icon="gui/icons/parachute-icon.png"/>
                     <spacer width="3%" height="100%"/>
                     <bubble proportion="1" height="100%"
                             I18N="In the help menu"

src/guiengine/skin.cpp

@@ -2416,14 +2416,14 @@ void Skin::drawBadgeOn(const Widget* widget, const core::recti& rect)
     if (widget->m_badges & ZIPPER_BADGE)
     {
         float max_icon_size = 0.43f;
-        video::ITexture* texture = irr_driver->getTexture(FileManager::MODEL,
+        video::ITexture* texture = irr_driver->getTexture(FileManager::GUI_ICON,
                                                           "zipper_collect.png");
         doDrawBadge(texture, rect, max_icon_size, false);
     }
     if (widget->m_badges & ANCHOR_BADGE)
     {
         float max_icon_size = 0.43f;
-        video::ITexture* texture = irr_driver->getTexture(FileManager::MODEL,
+        video::ITexture* texture = irr_driver->getTexture(FileManager::GUI_ICON,
                                                           "anchor-icon.png");
         doDrawBadge(texture, rect, max_icon_size, false);
     }

src/items/attachment_manager.cpp

@@ -23,6 +23,7 @@
 #include "graphics/material_manager.hpp"
 #include "graphics/sp/sp_base.hpp"
 #include "guiengine/engine.hpp"
+#include "guiengine/skin.hpp"
 #include "io/file_manager.hpp"
 
 AttachmentManager *attachment_manager = 0;
@@ -93,7 +94,8 @@ void AttachmentManager::loadModels()
         if(iat[i].icon_file)
         {
             std::string full_icon_path     =
-                file_manager->getAsset(FileManager::MODEL, iat[i].icon_file);
+                GUIEngine::getSkin()->getThemedIcon(std::string("gui/icons/")
+                                                    + iat[i].icon_file);
             m_all_icons[iat[i].attachment] =
                 material_manager->getMaterial(full_icon_path,
                                               /* full_path */     true,

src/items/powerup_manager.cpp

@@ -29,6 +29,7 @@
 #include "graphics/material.hpp"
 #include "graphics/material_manager.hpp"
 #include "guiengine/engine.hpp"
+#include "guiengine/skin.hpp"
 #include "io/file_manager.hpp"
 #include "io/xml_node.hpp"
 #include "items/bowling.hpp"
@@ -453,6 +454,7 @@ void PowerupManager::loadPowerup(PowerupType type, const XMLNode &node)
 {
     std::string icon_file("");
     node.get("icon", &icon_file);
+    icon_file = GUIEngine::getSkin()->getThemedIcon("gui/icons/" + icon_file);
 
 #ifdef DEBUG
     if (icon_file.size() == 0)
@@ -464,7 +466,7 @@ void PowerupManager::loadPowerup(PowerupType type, const XMLNode &node)
 #endif
 
     m_all_icons[type] = material_manager->getMaterial(icon_file,
-                                  /* full_path */     false,
+                                  /* full_path */     true,
                                   /*make_permanent */ true);