From 6bf0b64f248d143b53f4740f34009396bb05d49e Mon Sep 17 00:00:00 2001
From: Gleb Mazovetskiy <glex.spb@gmail.com>
Date: Thu, 20 Feb 2020 10:22:44 +0900
Subject: [PATCH] Support transparent images

---
 sdlutils.cpp | 21 ++++++++++++++++++++-
 viewer.cpp   | 20 +++++++++++++++-----
 2 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/sdlutils.cpp b/sdlutils.cpp
index 6ec0e47..752de54 100755
--- a/sdlutils.cpp
+++ b/sdlutils.cpp
@@ -34,6 +34,22 @@ SDL_Surface *SDL_utils::loadImage(const std::string &p_filename)
     return l_img2;
 }
 
+static void AsciiToLower(std::string *s)
+{
+    for (char &c : *s)
+        if (c >= 'A' && c <= 'Z')
+            c -= ('Z' - 'z');
+}
+
+static std::string GetFileExtension(const std::string &name) {
+    const auto dot_pos = name.rfind('.');
+    if (dot_pos == std::string::npos)
+        return "";
+    std::string ext = name.substr(dot_pos + 1);
+    AsciiToLower(&ext);
+    return ext;
+}
+
 SDL_Surface *SDL_utils::loadImageToFit(const std::string &p_filename, int fit_w, int fit_h)
 {
     // Load image
@@ -57,7 +73,10 @@ SDL_Surface *SDL_utils::loadImageToFit(const std::string &p_filename, int fit_w,
     target_h *= PPU_Y;
     SDL_Surface *l_img2 = zoomSurface(l_img, static_cast<double>(target_w) / l_img->w, static_cast<double>(target_h) / l_img->h, SMOOTHING_ON);
     SDL_FreeSurface(l_img);
-    SDL_Surface *l_img3 = SDL_DisplayFormat(l_img2);
+
+    const std::string ext = GetFileExtension(p_filename);
+    const bool supports_alpha = ext != "xcf" && ext != "jpg" && ext != "jpeg";
+    SDL_Surface *l_img3 = supports_alpha ? SDL_DisplayFormatAlpha(l_img2) : SDL_DisplayFormat(l_img2);
     SDL_FreeSurface(l_img2);
     return l_img3;
 }
diff --git a/viewer.cpp b/viewer.cpp
index 9398464..53c59d3 100755
--- a/viewer.cpp
+++ b/viewer.cpp
@@ -49,11 +49,7 @@ CViewer::CViewer(const std::string &p_fileName):
     // Create background image
     m_background = SDL_utils::createImage(SCREEN_WIDTH, SCREEN_HEIGHT * PPU_Y, SDL_MapRGB(Globals::g_screen->format, COLOR_BG_1));
     {
-        SDL_Rect l_rect;
-        l_rect.x = 0;
-        l_rect.y = 0;
-        l_rect.w = SCREEN_WIDTH;
-        l_rect.h = Y_LIST * PPU_Y;
+        SDL_Rect l_rect = {0, 0, SCREEN_WIDTH, Y_LIST * PPU_Y};
         SDL_FillRect(m_background, &l_rect, SDL_MapRGB(m_background->format, COLOR_BORDER));
     }
     // Print title
@@ -79,6 +75,20 @@ CViewer::CViewer(const std::string &p_fileName):
     if (m_image != nullptr)
     {
         m_mode = IMAGE;
+
+        // Transparency grid background.
+        constexpr int kTransparentBgRectSize = 10;
+        const Uint32 colors[2] = {
+            SDL_MapRGB(m_background->format, 240, 240, 240),
+            SDL_MapRGB(m_background->format, 155, 155, 155),
+        };
+        int i = 0;
+        for (int y = Y_LIST; y < SCREEN_HEIGHT; y += kTransparentBgRectSize, ++i) {
+            for (int x = 0; x < SCREEN_WIDTH; x += kTransparentBgRectSize, ++i) {
+                SDL_Rect rect = {x, y * PPU_Y, kTransparentBgRectSize, kTransparentBgRectSize * PPU_Y};
+                SDL_FillRect(m_background, &rect, colors[i % 2]);
+            }
+        }
     }
     else
     {