Fonts: ground work for allowing SizePixels to be optional.

imgui.cpp

@@ -1204,6 +1204,9 @@ CODE
 #define IMGUI_DEBUG_NAV_SCORING     0   // Display navigation scoring preview when hovering items. Hold CTRL to display for all candidates. CTRL+Arrow to change last direction.
 #define IMGUI_DEBUG_NAV_RECTS       0   // Display the reference navigation rectangle for each window
 
+// Default font size if unspecified in both style.FontSizeBase and AddFontXXX() calls.
+static const float FONT_DEFAULT_SIZE = 20.0f;
+
 // When using CTRL+TAB (or Gamepad Square+L/R) we delay the visual a little in order to reduce visual noise doing a fast switch.
 static const float NAV_WINDOWING_HIGHLIGHT_DELAY            = 0.20f;    // Time before the highlight and screen dimming starts fading in
 static const float NAV_WINDOWING_LIST_APPEAR_DELAY          = 0.15f;    // Time before the window list starts to appear
@@ -8635,7 +8638,7 @@ void ImGui::UpdateFontsNewFrame()
     // Apply default font size the first time
     ImFont* font = ImGui::GetDefaultFont();
     if (g.Style.FontSizeBase <= 0.0f)
-        g.Style.FontSizeBase = font->LegacySize * g.Style._MainScale;
+        g.Style.FontSizeBase = (font->LegacySize > 0.0f ? font->LegacySize : FONT_DEFAULT_SIZE) * g.Style._MainScale;
 
     // Set initial font
     g.Font = font;

imgui.h

@@ -3475,10 +3475,10 @@ struct ImFontConfig
     ImVec2          GlyphOffset;            // 0, 0     // Offset (in pixels) all glyphs from this font input. Absolute value for default size, other sizes will scale this value.
     float           GlyphMinAdvanceX;       // 0        // Minimum AdvanceX for glyphs, set Min to align font icons, set both Min/Max to enforce mono-space font. Absolute value for default size, other sizes will scale this value.
     float           GlyphMaxAdvanceX;       // FLT_MAX  // Maximum AdvanceX for glyphs
-    float           GlyphExtraAdvanceX;     // 0        // Extra spacing (in pixels) between glyphs. Please contact us if you are using this.
+    float           GlyphExtraAdvanceX;     // 0        // Extra spacing (in pixels) between glyphs. Please contact us if you are using this. // FIXME-NEWATLAS: Intentionally unscaled
     unsigned int    FontBuilderFlags;       // 0        // Settings for custom font builder. THIS IS BUILDER IMPLEMENTATION DEPENDENT. Leave as zero if unsure.
     float           RasterizerMultiply;     // 1.0f     // Linearly brighten (>1.0f) or darken (<1.0f) font output. Brightening small fonts may be a good workaround to make them more readable. This is a silly thing we may remove in the future.
-    float           RasterizerDensity;      // 1.0f     // (Legacy: this only makes sense when ImGuiBackendFlags_RendererHasTextures is not supported). DPI scale multiplier for rasterization. Not altering other font metrics: makes it easy to swap between e.g. a 100% and a 400% fonts for a zooming display, or handle Retina screen. IMPORTANT: If you change this it is expected that you increase/decrease font scale roughly to the inverse of this, otherwise quality may look lowered.
+    float           RasterizerDensity;      // 1.0f     // [LEGACY: this only makes sense when ImGuiBackendFlags_RendererHasTextures is not supported] DPI scale multiplier for rasterization. Not altering other font metrics: makes it easy to swap between e.g. a 100% and a 400% fonts for a zooming display, or handle Retina screen. IMPORTANT: If you change this it is expected that you increase/decrease font scale roughly to the inverse of this, otherwise quality may look lowered.
     ImWchar         EllipsisChar;           // 0        // Explicitly specify Unicode codepoint of ellipsis character. When fonts are being merged first specified ellipsis will be used.
 
     // [Internal]

imgui_draw.cpp

@@ -2988,10 +2988,13 @@ bool ImFontAtlas::Build()
 
 ImFont* ImFontAtlas::AddFont(const ImFontConfig* font_cfg_in)
 {
+    // Sanity Checks
     IM_ASSERT(!Locked && "Cannot modify a locked ImFontAtlas!");
     IM_ASSERT((font_cfg_in->FontData != NULL && font_cfg_in->FontDataSize > 0) || (font_cfg_in->FontLoader != NULL));
-    IM_ASSERT(font_cfg_in->SizePixels > 0.0f && "Is ImFontConfig struct correctly initialized?");
+    //IM_ASSERT(font_cfg_in->SizePixels > 0.0f && "Is ImFontConfig struct correctly initialized?");
     IM_ASSERT(font_cfg_in->RasterizerDensity > 0.0f && "Is ImFontConfig struct correctly initialized?");
+    if (font_cfg_in->GlyphOffset.x != 0.0f || font_cfg_in->GlyphOffset.y != 0.0f || font_cfg_in->GlyphMinAdvanceX != 0.0f || font_cfg_in->GlyphMaxAdvanceX != FLT_MAX)
+        IM_ASSERT(font_cfg_in->SizePixels != 0.0f && "Specifying glyph offset/advances requires a reference size to base it on.");
 
     // Lazily create builder on the first call to AddFont
     if (Builder == NULL)
@@ -4636,7 +4639,8 @@ static bool ImGui_ImplStbTrueType_FontBakedLoadGlyph(ImFontAtlas* atlas, ImFontC
         if (oversample_v > 1)
             stbtt__v_prefilter(bitmap_pixels, r->w, r->h, r->w, oversample_v);
 
-        const float offsets_scale = baked->Size / baked->ContainerFont->Sources[0]->SizePixels;
+        const float ref_size = baked->ContainerFont->Sources[0]->SizePixels;
+        const float offsets_scale = (ref_size != 0.0f) ? (baked->Size / ref_size) : 1.0f;
         float font_off_x = (src->GlyphOffset.x * offsets_scale);
         float font_off_y = (src->GlyphOffset.y * offsets_scale);
         if (src->PixelSnapH) // Snap scaled offset. This is to mitigate backward compatibility issues for GlyphOffset, but a better design would be welcome.
@@ -5075,7 +5079,8 @@ ImFontGlyph* ImFontAtlasBakedAddFontGlyph(ImFontAtlas* atlas, ImFontBaked* baked
     if (src != NULL)
     {
         // Clamp & recenter if needed
-        const float offsets_scale = baked->Size / baked->ContainerFont->Sources[0]->SizePixels;
+        const float ref_size = baked->ContainerFont->Sources[0]->SizePixels;
+        const float offsets_scale = (ref_size != 0.0f) ? (baked->Size / ref_size) : 1.0f;
         float advance_x = ImClamp(glyph->AdvanceX, src->GlyphMinAdvanceX * offsets_scale, src->GlyphMaxAdvanceX * offsets_scale);
         if (advance_x != glyph->AdvanceX)
         {

misc/freetype/imgui_freetype.cpp

@@ -527,7 +527,8 @@ bool ImGui_ImplFreeType_FontBakedLoadGlyph(ImFontAtlas* atlas, ImFontConfig* src
         uint32_t* temp_buffer = (uint32_t*)atlas->Builder->TempBuffer.Data;
         ImGui_ImplFreeType_BlitGlyph(ft_bitmap, temp_buffer, w);
 
-        const float offsets_scale = baked->Size / baked->ContainerFont->Sources[0]->SizePixels;
+        const float ref_size = baked->ContainerFont->Sources[0]->SizePixels;
+        const float offsets_scale = (ref_size != 0.0f) ? (baked->Size / ref_size) : 1.0f;
         float font_off_x = (src->GlyphOffset.x * offsets_scale);
         float font_off_y = (src->GlyphOffset.y * offsets_scale) + baked->Ascent;
         if (src->PixelSnapH) // Snap scaled offset. This is to mitigate backward compatibility issues for GlyphOffset, but a better design would be welcome.