Add selection background to IME rendering

Decided to implement it anyway since the broken behavior (selection
length always being 0, at least on Windows) may get fixed later in SDL,
so let's do it right in one go.

desktop_version/src/IMERender.cpp

@@ -4,6 +4,7 @@
 #include "Font.h"
 #include "Graphics.h"
 #include "KeyPoll.h"
+#include "UTF8.h"
 
 static bool render_done = false;
 static SDL_Rect imebox;
@@ -31,6 +32,53 @@ void ime_render(void)
 
     graphics.fill_rect(&imebox_border, 128, 128, 128);
     graphics.fill_rect(&imebox, 0, 0, 0);
+
+    if (key.imebuffer_length > 0)
+    {
+        /* Also show a selection, so we need to know where and how long it is...
+         * Because SDL gives us the number of "characters" (so, codepoints)... */
+        const char* imebuffer_ptr = key.imebuffer.c_str();
+        const char* sel_start_ptr = imebuffer_ptr;
+        for (int i = 0; i < key.imebuffer_start; i++)
+        {
+            if (UTF8_next(&sel_start_ptr) == 0)
+            {
+                // Already past the '\0'...
+                sel_start_ptr--;
+                break;
+            }
+        }
+        const char* sel_end_ptr = sel_start_ptr;
+        for (int i = 0; i < key.imebuffer_length; i++)
+        {
+            if (UTF8_next(&sel_end_ptr) == 0)
+            {
+                break;
+            }
+        }
+        size_t before_sel_nbytes = sel_start_ptr - imebuffer_ptr;
+        size_t in_sel_nbytes = sel_end_ptr - sel_start_ptr;
+        char* before_sel = (char*) SDL_malloc(before_sel_nbytes + 1);
+        char* in_sel = (char*) SDL_malloc(in_sel_nbytes + 1);
+        if (before_sel != NULL && in_sel != NULL)
+        {
+            SDL_memcpy(before_sel, imebuffer_ptr, before_sel_nbytes);
+            before_sel[before_sel_nbytes] = '\0';
+            SDL_memcpy(in_sel, sel_start_ptr, in_sel_nbytes);
+            in_sel[in_sel_nbytes] = '\0';
+
+            int before_sel_pixels = font::len(PR_FONT_LEVEL, before_sel);
+            int in_sel_pixels = font::len(PR_FONT_LEVEL, in_sel);
+
+            SDL_Rect selrect = imebox;
+            selrect.x += before_sel_pixels + 1;
+            selrect.w = in_sel_pixels;
+            graphics.fill_rect(&selrect, 128, 64, 0);
+        }
+        SDL_free(before_sel);
+        SDL_free(in_sel);
+    }
+
     font::print(PR_FONT_LEVEL | PR_CJK_LOW, imebox.x + 1, imebox.y + 1, key.imebuffer, 255, 255, 255);
 
     render_done = true;

desktop_version/src/KeyPoll.cpp

@@ -52,6 +52,8 @@ KeyPoll::KeyPoll(void)
 
     keybuffer = "";
     imebuffer = "";
+    imebuffer_start = 0;
+    imebuffer_length = 0;
     leftbutton=0; rightbutton=0; middlebutton=0;
     mousex = 0;
     mousey = 0;
@@ -67,6 +69,8 @@ void KeyPoll::enabletextentry(void)
 {
     keybuffer = "";
     imebuffer = "";
+    imebuffer_start = 0;
+    imebuffer_length = 0;
     SDL_StartTextInput();
 }
 
@@ -74,6 +78,8 @@ void KeyPoll::disabletextentry(void)
 {
     SDL_StopTextInput();
     imebuffer = "";
+    imebuffer_start = 0;
+    imebuffer_length = 0;
 }
 
 bool KeyPoll::textentry(void)
@@ -326,9 +332,13 @@ void KeyPoll::Poll(void)
             break;
         case SDL_TEXTEDITING:
             imebuffer = evt.edit.text;
+            imebuffer_start = evt.edit.start;
+            imebuffer_length = evt.edit.length;
             break;
         case SDL_TEXTEDITING_EXT:
             imebuffer = evt.editExt.text;
+            imebuffer_start = evt.editExt.start;
+            imebuffer_length = evt.editExt.length;
             SDL_free(evt.editExt.text);
             break;
 

desktop_version/src/KeyPoll.h

@@ -70,6 +70,8 @@ public:
     bool pressedbackspace;
     std::string keybuffer;
     std::string imebuffer;
+    int imebuffer_start;
+    int imebuffer_length;
 
     bool linealreadyemptykludge;