From 0a6b1ea256e2756da4170a32f2914f78e8d7e45e Mon Sep 17 00:00:00 2001
From: Jon Evans <jon@craftyjon.com>
Date: Mon, 27 May 2019 12:35:05 -0400
Subject: [PATCH] Improve image alpha handling in PDF and PS plotters

Fixes: lp:1825276
* https://bugs.launchpad.net/kicad/+bug/1825276

(cherry picked from commit 4adf89b40b4e471533fb07860a82c5f65133a3b8)
---
 common/plotters/PDF_plotter.cpp | 15 +++++++++++++++
 common/plotters/PS_plotter.cpp  | 14 ++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/common/plotters/PDF_plotter.cpp b/common/plotters/PDF_plotter.cpp
index 6e29188b52..cde9f51795 100644
--- a/common/plotters/PDF_plotter.cpp
+++ b/common/plotters/PDF_plotter.cpp
@@ -390,6 +390,21 @@ void PDF_PLOTTER::PlotImage( const wxImage & aImage, const wxPoint& aPos,
             unsigned char r = aImage.GetRed( x, y ) & 0xFF;
             unsigned char g = aImage.GetGreen( x, y ) & 0xFF;
             unsigned char b = aImage.GetBlue( x, y ) & 0xFF;
+
+            // PDF inline images don't support alpha, so premultiply against white background
+            if( aImage.HasAlpha() )
+            {
+                unsigned char alpha = aImage.GetAlpha( x, y ) & 0xFF;
+
+                if( alpha < 0xFF )
+                {
+                    float a = 1.0 - ( (float) alpha / 255.0 );
+                    r = ( int )( r + ( a * 0xFF ) ) & 0xFF;
+                    g = ( int )( g + ( a * 0xFF ) ) & 0xFF;
+                    b = ( int )( b + ( a * 0xFF ) ) & 0xFF;
+                }
+            }
+
             // As usual these days, stdio buffering has to suffeeeeerrrr
             if( colorMode )
             {
diff --git a/common/plotters/PS_plotter.cpp b/common/plotters/PS_plotter.cpp
index ac13d2826c..46f7fc174a 100644
--- a/common/plotters/PS_plotter.cpp
+++ b/common/plotters/PS_plotter.cpp
@@ -709,6 +709,20 @@ void PS_PLOTTER::PlotImage( const wxImage & aImage, const wxPoint& aPos,
             green = aImage.GetGreen( xx, yy) & 0xFF;
             blue = aImage.GetBlue( xx, yy) & 0xFF;
 
+            // PS doesn't support alpha, so premultiply against white background
+            if( aImage.HasAlpha() )
+            {
+                unsigned char alpha = aImage.GetAlpha( xx, yy ) & 0xFF;
+
+                if( alpha < 0xFF )
+                {
+                    float a = 1.0 - ( (float) alpha / 255.0 );
+                    red =   ( int )( red   + ( a * 0xFF ) ) & 0xFF;
+                    green = ( int )( green + ( a * 0xFF ) ) & 0xFF;
+                    blue =  ( int )( blue  + ( a * 0xFF ) ) & 0xFF;
+                }
+            }
+
             if( colorMode )
                 fprintf( outputFile, "%2.2X%2.2X%2.2X", red, green, blue );
             else