Add shader to render ghost kart

data/shaders/ge_shaders/ghost.frag

@@ -0,0 +1,13 @@
+layout(location = 0) in vec4 f_vertex_color;
+layout(location = 1) in vec2 f_uv;
+layout(location = 3) flat in int f_material_id;
+
+layout(location = 0) out vec4 o_color;
+
+#include "utils/sample_mesh_texture.h"
+
+void main()
+{
+    vec3 mixed_color = sampleMeshTexture0(f_material_id, f_uv).xyz * f_vertex_color.xyz;
+    o_color = vec4(mixed_color * 0.5, 0.5);
+}

lib/graphics_engine/src/ge_vulkan_draw_call.cpp

@@ -257,6 +257,7 @@ std::string GEVulkanDrawCall::getShader(irr::scene::ISceneNode* node,
     case irr::video::EMT_ONETEXTURE_BLEND: return "alphablend";
     case irr::video::EMT_SOLID_2_LAYER: return "decal";
     case irr::video::EMT_STK_GRASS: return "grass";
+    case irr::video::EMT_STK_GHOST: return "ghost";
     default: return "solid";
     }
 }   // getShader
@@ -308,9 +309,17 @@ void GEVulkanDrawCall::createAllPipelines(GEVulkanDriver* vk)
     settings.m_vertex_shader = "spm.vert";
     settings.m_skinning_vertex_shader = "spm_skinning.vert";
     settings.m_push_constants_func = nullptr;
+
+    settings.m_depth_write = true;
+    settings.m_backface_culling = true;
+    settings.m_alphablend = true;
+    settings.m_drawing_priority = (char)9;
+    settings.m_fragment_shader = "ghost.frag";
+    settings.m_shader_name = "ghost";
+    createPipeline(vk, settings);
+
     settings.m_depth_write = false;
     settings.m_backface_culling = false;
-    settings.m_alphablend = true;
     settings.m_drawing_priority = (char)10;
 
     settings.m_fragment_shader = "transparent.frag";

lib/irrlicht/include/EMaterialTypes.h

@@ -195,6 +195,9 @@ namespace video
 		//! Alphatest material for grass without using vertex color in stk. */
 		EMT_STK_GRASS,
 
+		//! Render objects like ghost in stk (used by ghost karts for now). */
+		EMT_STK_GHOST,
+
 		//! This value is not used. It only forces this enumeration to compile to 32 bit.
 		EMT_FORCE_32BIT = 0x7fffffff
 	};

src/karts/ghost_kart.cpp

@@ -22,6 +22,7 @@
 #include "karts/controller/ghost_controller.hpp"
 #include "karts/kart_gfx.hpp"
 #include "karts/kart_model.hpp"
+#include "graphics/irr_driver.hpp"
 #include "graphics/render_info.hpp"
 #include "modes/easter_egg_hunt.hpp"
 #include "modes/linear_world.hpp"
@@ -45,6 +46,8 @@ GhostKart::GhostKart(const std::string& ident, unsigned int world_kart_id,
 // ----------------------------------------------------------------------------
 void GhostKart::reset()
 {
+    m_current_attachment = -1;
+    m_graphical_y_offset = 0;
     m_node->setVisible(true);
     Kart::reset();
     // This will set the correct start position
@@ -80,6 +83,44 @@ void GhostKart::addReplayEvent(float time,
 
 }   // addReplayEvent
 
+// ----------------------------------------------------------------------------
+void GhostKart::setGhostKartMaterial()
+{
+    if (irr_driver->getVideoDriver()->getDriverType() != video::EDT_VULKAN ||
+        m_current_attachment == (int)m_attachment->getType())
+        return;
+
+    m_current_attachment = (int)m_attachment->getType();
+    std::function<void(core::array<scene::ISceneNode*>&)> set_ghost =
+    [&](core::array<scene::ISceneNode*>& child)
+    {
+        for (unsigned i = 0; i < child.size(); i++)
+        {
+            scene::ISceneNode* node = child[i];
+            if (node->getType() != irr::scene::ESNT_ANIMATED_MESH &&
+                node->getType() != irr::scene::ESNT_MESH)
+                continue;
+            if (node->getType() == scene::ESNT_ANIMATED_MESH)
+            {
+                scene::IAnimatedMeshSceneNode* anode = static_cast<
+                    scene::IAnimatedMeshSceneNode*>(node);
+                anode->setReadOnlyMaterials(false);
+                for (unsigned j = 0; j < anode->getJointCount(); j++)
+                    set_ghost(anode->getJointNode(j)->getChildren());
+            }
+            else if (node->getType() == scene::ESNT_MESH)
+            {
+                static_cast<scene::IMeshSceneNode*>(node)
+                    ->setReadOnlyMaterials(false);
+            }
+            for (unsigned j = 0; j < node->getMaterialCount(); j++)
+                node->getMaterial(j).MaterialType = video::EMT_STK_GHOST;
+            set_ghost(node->getChildren());
+        }
+    };
+    set_ghost(m_node->getChildren());
+}   // setGhostKartMaterial
+
 // ----------------------------------------------------------------------------
 /** Called once per rendered frame. It is used to only update any graphical
  *  effects.
@@ -96,6 +137,7 @@ void GhostKart::updateGraphics(float dt)
     Moveable::updateGraphics(center_shift, btQuaternion(0, 0, 0, 1));
     // Also update attachment's graphics
     m_attachment->updateGraphics(dt);
+    setGhostKartMaterial();
 }   // updateGraphics
 
 // ----------------------------------------------------------------------------

src/karts/ghost_kart.hpp

@@ -50,10 +50,12 @@ private:
 
     unsigned int                             m_last_egg_idx = 0;
 
+    int m_current_attachment;
     // ----------------------------------------------------------------------------
     /** Compute the time at which the ghost finished the race */
     void          computeFinishTime();
-
+    // ----------------------------------------------------------------------------
+    void setGhostKartMaterial();
 public:
                   GhostKart(const std::string& ident, unsigned int world_kart_id,
                             int position, float color_hue,