ImFont::RenderText() better vertical clipping for large amount of text (for #200)

imgui.cpp

@@ -10023,21 +10023,25 @@ void ImFont::RenderText(float size, ImVec2 pos, ImU32 col, const ImVec4& clip_re
     if (!text_end)
         text_end = text_begin + strlen(text_begin);
 
-    const float scale = size / FontSize;
-    const float line_height = FontSize * scale;
-
     // Align to be pixel perfect
     pos.x = (float)(int)pos.x + DisplayOffset.x;
     pos.y = (float)(int)pos.y + DisplayOffset.y;
     float x = pos.x;
     float y = pos.y;
+    if (y > clip_rect.w)
+        return;
 
+    const float scale = size / FontSize;
+    const float line_height = FontSize * scale;
     const bool word_wrap_enabled = (wrap_width > 0.0f);
     const char* word_wrap_eol = NULL;
 
     ImDrawVert* out_vertices = draw_list->vtx_write;
 
     const char* s = text_begin;
+    if (!word_wrap_enabled && y + line_height < clip_rect.y)
+        while (s < text_end && *s != '\n')  // Fast-forward to next line
+            s++;
     while (s < text_end)
     {
         if (word_wrap_enabled)
@@ -10085,6 +10089,13 @@ void ImFont::RenderText(float size, ImVec2 pos, ImU32 col, const ImVec4& clip_re
             {
                 x = pos.x;
                 y += line_height;
+
+                if (y > clip_rect.w)
+                    break;
+                if (!word_wrap_enabled && y + line_height < clip_rect.y)
+                    while (s < text_end && *s != '\n')  // Fast-forward to next line
+                        s++;
+
                 continue;
             }
             if (c == '\r')
@@ -10095,21 +10106,14 @@ void ImFont::RenderText(float size, ImVec2 pos, ImU32 col, const ImVec4& clip_re
         if (const Glyph* glyph = FindGlyph((unsigned short)c))
         {
             char_width = glyph->XAdvance * scale;
+            
+            // Clipping on Y is more likely
             if (c != ' ' && c != '\t')
             {
-                // Clipping on Y is more likely
+                // We don't do a second finer clipping test on the Y axis (todo: do some measurement see if it is worth it, probably not)
                 float y1 = (float)(y + glyph->YOffset * scale);
-                if (y1 > clip_rect.w)
-                    break;
                 float y2 = (float)(y1 + glyph->Height * scale);
-                if (y2 < clip_rect.y)
-                {
-                    // Fast-forward until next line
-                    char_width = 0.0f;
-                    while (s < text_end && *s != '\n') s++;
-                }
-                else
-                {
+
                 float x1 = (float)(x + glyph->XOffset * scale);
                 float x2 = (float)(x1 + glyph->Width * scale);
                 if (x1 <= clip_rect.z && x2 >= clip_rect.x)
@@ -10169,7 +10173,6 @@ void ImFont::RenderText(float size, ImVec2 pos, ImU32 col, const ImVec4& clip_re
                 }
             }
         }
-        }
 
         x += char_width;
     }