From 6936f30b36e6f000aac685c658ecae541e2587c5 Mon Sep 17 00:00:00 2001
From: Vincent Lejeune <vljn@ovi.com>
Date: Sat, 10 May 2014 20:49:30 +0200
Subject: [PATCH] Premultiply alpha for billboards.

---
 data/shaders/billboard.frag   |  2 +-
 src/graphics/glwrap.cpp       | 15 +++++++++++++--
 src/graphics/glwrap.hpp       |  2 +-
 src/graphics/stkbillboard.cpp |  2 +-
 4 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/data/shaders/billboard.frag b/data/shaders/billboard.frag
index 6df5ad558..0eb0af806 100644
--- a/data/shaders/billboard.frag
+++ b/data/shaders/billboard.frag
@@ -12,5 +12,5 @@ varying vec2 uv;
 void main(void)
 {
     vec4 color = texture(tex, uv);
-    FragColor = vec4(color.rgb * color.a, color.a);
+    FragColor = vec4(color.rgb, color.a);
 }
diff --git a/src/graphics/glwrap.cpp b/src/graphics/glwrap.cpp
index 996760e02..aacb64ba2 100644
--- a/src/graphics/glwrap.cpp
+++ b/src/graphics/glwrap.cpp
@@ -315,7 +315,7 @@ void resetTextureTable()
     AlreadyTransformedTexture.clear();
 }
 
-void compressTexture(irr::video::ITexture *tex, bool srgb)
+void compressTexture(irr::video::ITexture *tex, bool srgb, bool premul_alpha)
 {
     if (AlreadyTransformedTexture.find(tex) != AlreadyTransformedTexture.end())
         return;
@@ -338,7 +338,7 @@ void compressTexture(irr::video::ITexture *tex, bool srgb)
     }
 
     size_t w = tex->getSize().Width, h = tex->getSize().Height;
-    char *data = new char[w * h * 4];
+    unsigned char *data = new unsigned char[w * h * 4];
     memcpy(data, tex->lock(), w * h * 4);
     tex->unlock();
     unsigned internalFormat, Format;
@@ -347,6 +347,17 @@ void compressTexture(irr::video::ITexture *tex, bool srgb)
     else
         Format = GL_BGR;
 
+    if (premul_alpha)
+    {
+        for (unsigned i = 0; i < w * h; i++)
+        {
+            float alpha = pow(data[4 * i + 3] / 255., 1. / 2.2);
+            data[4 * i] *= alpha;
+            data[4 * i + 1] *= alpha;
+            data[4 * i + 2] *= alpha;
+        }
+    }
+
     if (!UserConfigParams::m_texture_compression)
     {
         if (srgb)
diff --git a/src/graphics/glwrap.hpp b/src/graphics/glwrap.hpp
index 5cec12f90..bd64792d7 100644
--- a/src/graphics/glwrap.hpp
+++ b/src/graphics/glwrap.hpp
@@ -181,7 +181,7 @@ public:
 GLuint getTextureGLuint(irr::video::ITexture *tex);
 GLuint getDepthTexture(irr::video::ITexture *tex);
 void resetTextureTable();
-void compressTexture(irr::video::ITexture *tex, bool srgb);
+void compressTexture(irr::video::ITexture *tex, bool srgb, bool premul_alpha = false);
 bool loadCompressedTexture(const std::string& compressed_tex);
 void saveCompressedTexture(const std::string& compressed_tex);
 void blitFBO(GLuint Src, GLuint Dst, size_t width, size_t height);
diff --git a/src/graphics/stkbillboard.cpp b/src/graphics/stkbillboard.cpp
index 7b71977b5..4ce29f479 100644
--- a/src/graphics/stkbillboard.cpp
+++ b/src/graphics/stkbillboard.cpp
@@ -35,7 +35,7 @@ void STKBillboard::render()
     core::vector3df pos = getAbsolutePosition();
     glBindVertexArray(billboardvao);
     video::ITexture *tex = Material.getTexture(0);
-    compressTexture(tex, true);
+    compressTexture(tex, true, true);
     GLuint texid = getTextureGLuint(tex);
     setTexture(0, texid, GL_LINEAR, GL_LINEAR);
     glUseProgram(MeshShader::BillboardShader::Program);