Make font atlas packing padding configurable

imgui.h

@@ -1382,6 +1382,7 @@ struct ImFontAtlas
     int                         TexWidth;           // Texture width calculated during Build().
     int                         TexHeight;          // Texture height calculated during Build().
     int                         TexDesiredWidth;    // Texture width desired by user before Build(). Must be a power-of-two. If have many glyphs your graphics API have texture size restrictions you may want to increase texture width to decrease height.
+	int                         TexGlyphPadding;    // Padding between glyphs within texture in pixels. Defaults to 1.
     ImVec2                      TexUvWhitePixel;    // Texture coordinates to a white pixel
     ImVector<ImFont*>           Fonts;              // Hold all the fonts returned by AddFont*. Fonts[0] is the default font upon calling ImGui::NewFrame(), use ImGui::PushFont()/PopFont() to change the current font.
 

imgui_draw.cpp

@@ -1061,6 +1061,7 @@ ImFontAtlas::ImFontAtlas()
     TexPixelsAlpha8 = NULL;
     TexPixelsRGBA32 = NULL;
     TexWidth = TexHeight = TexDesiredWidth = 0;
+	TexGlyphPadding = 1;
     TexUvWhitePixel = ImVec2(0, 0);
 }
 
@@ -1314,13 +1315,13 @@ bool    ImFontAtlas::Build()
         }
     }
 
-    // Start packing. We need a known width for the skyline algorithm. Using a cheap heuristic here to decide of width. User can override TexDesiredWidth if they wish.
+    // Start packing. We need a known width for the skyline algorithm. Using a cheap heuristic here to decide of width. User can override TexDesiredWidth and TexGlyphPadding if they wish.
     // After packing is done, width shouldn't matter much, but some API/GPU have texture size limitations and increasing width can decrease height.
     TexWidth = (TexDesiredWidth > 0) ? TexDesiredWidth : (total_glyph_count > 4000) ? 4096 : (total_glyph_count > 2000) ? 2048 : (total_glyph_count > 1000) ? 1024 : 512;
     TexHeight = 0;
     const int max_tex_height = 1024*32;
     stbtt_pack_context spc;
-    stbtt_PackBegin(&spc, NULL, TexWidth, max_tex_height, 0, 1, NULL);
+    stbtt_PackBegin(&spc, NULL, TexWidth, max_tex_height, 0, TexGlyphPadding, NULL);
 
     // Pack our extra data rectangles first, so it will be on the upper-left corner of our texture (UV will have small values).
     ImVector<stbrp_rect> extra_rects;