perf: Port upstream font drawing performance optimization (PR #978)

Cherry-pick upstream commit 07d715e which refactors renderChar and
drawTextRotated90CW into a template-based renderCharImpl, hoisting
the is2Bit branch outside inner pixel loops for 15-23% speedup.

Additionally extends the template with Rotated90CCW to fix two bugs
in the mod's drawTextRotated90CCW: operator precedence in bmpVal
calculation and missing compressed font support via getGlyphBitmap.

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/GfxRenderer/GfxRenderer.cpp

@@ -59,6 +59,130 @@ static inline void rotateCoordinates(const GfxRenderer::Orientation orientation,
   }
 }
 
+enum class TextRotation { None, Rotated90CW, Rotated90CCW };
+
+// Shared glyph rendering logic for normal and rotated text.
+// Coordinate mapping and cursor advance direction are selected at compile time via the template parameter.
+template <TextRotation rotation>
+static void renderCharImpl(const GfxRenderer& renderer, GfxRenderer::RenderMode renderMode,
+                           const EpdFontFamily& fontFamily, const uint32_t cp, int* cursorX, int* cursorY,
+                           const bool pixelState, const EpdFontFamily::Style style) {
+  const EpdGlyph* glyph = fontFamily.getGlyph(cp, style);
+  if (!glyph) {
+    glyph = fontFamily.getGlyph(REPLACEMENT_GLYPH, style);
+  }
+
+  if (!glyph) {
+    LOG_ERR("GFX", "No glyph for codepoint %d", cp);
+    return;
+  }
+
+  const EpdFontData* fontData = fontFamily.getData(style);
+  const bool is2Bit = fontData->is2Bit;
+  const uint8_t width = glyph->width;
+  const uint8_t height = glyph->height;
+  const int left = glyph->left;
+  const int top = glyph->top;
+
+  const uint8_t* bitmap = renderer.getGlyphBitmap(fontData, glyph);
+
+  if (bitmap != nullptr) {
+    int outerBase, innerBase;
+    if constexpr (rotation == TextRotation::Rotated90CW) {
+      outerBase = *cursorX + fontData->ascender - top;  // screenX = outerBase + glyphY
+      innerBase = *cursorY - left;                      // screenY = innerBase - glyphX
+    } else if constexpr (rotation == TextRotation::Rotated90CCW) {
+      outerBase = *cursorX + fontData->advanceY - 1 - fontData->ascender + top;  // screenX = outerBase - glyphY
+      innerBase = *cursorY + left;                                               // screenY = innerBase + glyphX
+    } else {
+      outerBase = *cursorY - top;   // screenY = outerBase + glyphY
+      innerBase = *cursorX + left;  // screenX = innerBase + glyphX
+    }
+
+    if (is2Bit) {
+      int pixelPosition = 0;
+      for (int glyphY = 0; glyphY < height; glyphY++) {
+        int outerCoord;
+        if constexpr (rotation == TextRotation::Rotated90CCW) {
+          outerCoord = outerBase - glyphY;
+        } else {
+          outerCoord = outerBase + glyphY;
+        }
+        for (int glyphX = 0; glyphX < width; glyphX++, pixelPosition++) {
+          int screenX, screenY;
+          if constexpr (rotation == TextRotation::Rotated90CW) {
+            screenX = outerCoord;
+            screenY = innerBase - glyphX;
+          } else if constexpr (rotation == TextRotation::Rotated90CCW) {
+            screenX = outerCoord;
+            screenY = innerBase + glyphX;
+          } else {
+            screenX = innerBase + glyphX;
+            screenY = outerCoord;
+          }
+
+          const uint8_t byte = bitmap[pixelPosition >> 2];
+          const uint8_t bit_index = (3 - (pixelPosition & 3)) * 2;
+          // the direct bit from the font is 0 -> white, 1 -> light gray, 2 -> dark gray, 3 -> black
+          // we swap this to better match the way images and screen think about colors:
+          // 0 -> black, 1 -> dark grey, 2 -> light grey, 3 -> white
+          const uint8_t bmpVal = 3 - ((byte >> bit_index) & 0x3);
+
+          if (renderMode == GfxRenderer::BW && bmpVal < 3) {
+            // Black (also paints over the grays in BW mode)
+            renderer.drawPixel(screenX, screenY, pixelState);
+          } else if (renderMode == GfxRenderer::GRAYSCALE_MSB && (bmpVal == 1 || bmpVal == 2)) {
+            // Light gray (also mark the MSB if it's going to be a dark gray too)
+            // We have to flag pixels in reverse for the gray buffers, as 0 leave alone, 1 update
+            renderer.drawPixel(screenX, screenY, false);
+          } else if (renderMode == GfxRenderer::GRAYSCALE_LSB && bmpVal == 1) {
+            // Dark gray
+            renderer.drawPixel(screenX, screenY, false);
+          }
+        }
+      }
+    } else {
+      int pixelPosition = 0;
+      for (int glyphY = 0; glyphY < height; glyphY++) {
+        int outerCoord;
+        if constexpr (rotation == TextRotation::Rotated90CCW) {
+          outerCoord = outerBase - glyphY;
+        } else {
+          outerCoord = outerBase + glyphY;
+        }
+        for (int glyphX = 0; glyphX < width; glyphX++, pixelPosition++) {
+          int screenX, screenY;
+          if constexpr (rotation == TextRotation::Rotated90CW) {
+            screenX = outerCoord;
+            screenY = innerBase - glyphX;
+          } else if constexpr (rotation == TextRotation::Rotated90CCW) {
+            screenX = outerCoord;
+            screenY = innerBase + glyphX;
+          } else {
+            screenX = innerBase + glyphX;
+            screenY = outerCoord;
+          }
+
+          const uint8_t byte = bitmap[pixelPosition >> 3];
+          const uint8_t bit_index = 7 - (pixelPosition & 7);
+
+          if ((byte >> bit_index) & 1) {
+            renderer.drawPixel(screenX, screenY, pixelState);
+          }
+        }
+      }
+    }
+  }
+
+  if constexpr (rotation == TextRotation::Rotated90CW) {
+    *cursorY -= glyph->advanceX;
+  } else if constexpr (rotation == TextRotation::Rotated90CCW) {
+    *cursorY += glyph->advanceX;
+  } else {
+    *cursorX += glyph->advanceX;
+  }
+}
+
 // IMPORTANT: This function is in critical rendering path and is called for every pixel. Please keep it as simple and
 // efficient as possible.
 void GfxRenderer::drawPixel(const int x, const int y, const bool state) const {
@@ -115,7 +239,7 @@ void GfxRenderer::drawCenteredText(const int fontId, const int y, const char* te
 
 void GfxRenderer::drawText(const int fontId, const int x, const int y, const char* text, const bool black,
                            const EpdFontFamily::Style style) const {
-  const int yPos = y + getFontAscenderSize(fontId);
+  int yPos = y + getFontAscenderSize(fontId);
   int xpos = x;
 
   // cannot draw a NULL / empty string
@@ -890,68 +1014,12 @@ void GfxRenderer::drawTextRotated90CW(const int fontId, const int x, const int y
 
   const auto& font = fontIt->second;
 
-  // For 90° clockwise rotation:
+  int xPos = x;
-  // Original (glyphX, glyphY) -> Rotated (glyphY, -glyphX)
+  int yPos = y;
-  // Text reads from bottom to top
-
-  int yPos = y;  // Current Y position (decreases as we draw characters)
 
   uint32_t cp;
   while ((cp = utf8NextCodepoint(reinterpret_cast<const uint8_t**>(&text)))) {
-    const EpdGlyph* glyph = font.getGlyph(cp, style);
+    renderCharImpl<TextRotation::Rotated90CW>(*this, renderMode, font, cp, &xPos, &yPos, black, style);
-    if (!glyph) {
-      glyph = font.getGlyph(REPLACEMENT_GLYPH, style);
-    }
-    if (!glyph) {
-      continue;
-    }
-
-    const EpdFontData* fontData = font.getData(style);
-    const int is2Bit = fontData->is2Bit;
-    const uint8_t width = glyph->width;
-    const uint8_t height = glyph->height;
-    const int left = glyph->left;
-    const int top = glyph->top;
-
-    const uint8_t* bitmap = getGlyphBitmap(fontData, glyph);
-
-    if (bitmap != nullptr) {
-      for (int glyphY = 0; glyphY < height; glyphY++) {
-        for (int glyphX = 0; glyphX < width; glyphX++) {
-          const int pixelPosition = glyphY * width + glyphX;
-
-          // 90° clockwise rotation transformation:
-          // screenX = x + (ascender - top + glyphY)
-          // screenY = yPos - (left + glyphX)
-          const int screenX = x + (fontData->ascender - top + glyphY);
-          const int screenY = yPos - left - glyphX;
-
-          if (is2Bit) {
-            const uint8_t byte = bitmap[pixelPosition / 4];
-            const uint8_t bit_index = (3 - pixelPosition % 4) * 2;
-            const uint8_t bmpVal = 3 - (byte >> bit_index) & 0x3;
-
-            if (renderMode == BW && bmpVal < 3) {
-              drawPixel(screenX, screenY, black);
-            } else if (renderMode == GRAYSCALE_MSB && (bmpVal == 1 || bmpVal == 2)) {
-              drawPixel(screenX, screenY, false);
-            } else if (renderMode == GRAYSCALE_LSB && bmpVal == 1) {
-              drawPixel(screenX, screenY, false);
-            }
-          } else {
-            const uint8_t byte = bitmap[pixelPosition / 8];
-            const uint8_t bit_index = 7 - (pixelPosition % 8);
-
-            if ((byte >> bit_index) & 1) {
-              drawPixel(screenX, screenY, black);
-            }
-          }
-        }
-      }
-    }
-
-    // Move to next character position (going up, so decrease Y)
-    yPos -= glyph->advanceX;
   }
 }
 
@@ -962,77 +1030,20 @@ void GfxRenderer::drawTextRotated90CCW(const int fontId, const int x, const int
     return;
   }
 
-  if (fontMap.count(fontId) == 0) {
+  const auto fontIt = fontMap.find(fontId);
+  if (fontIt == fontMap.end()) {
     LOG_ERR("GFX", "Font %d not found", fontId);
     return;
   }
-  const auto font = fontMap.at(fontId);
 
-  // For 90° counter-clockwise rotation:
+  const auto& font = fontIt->second;
-  // Mirror of CW: glyphY maps to -X direction, glyphX maps to +Y direction
-  // Text reads from top to bottom
 
-  const int advanceY = font.getData(style)->advanceY;
+  int xPos = x;
-  const int ascender = font.getData(style)->ascender;
+  int yPos = y;
-
-  int yPos = y;  // Current Y position (increases as we draw characters)
 
   uint32_t cp;
   while ((cp = utf8NextCodepoint(reinterpret_cast<const uint8_t**>(&text)))) {
-    const EpdGlyph* glyph = font.getGlyph(cp, style);
+    renderCharImpl<TextRotation::Rotated90CCW>(*this, renderMode, font, cp, &xPos, &yPos, black, style);
-    if (!glyph) {
-      glyph = font.getGlyph(REPLACEMENT_GLYPH, style);
-    }
-    if (!glyph) {
-      continue;
-    }
-
-    const int is2Bit = font.getData(style)->is2Bit;
-    const uint32_t offset = glyph->dataOffset;
-    const uint8_t width = glyph->width;
-    const uint8_t height = glyph->height;
-    const int left = glyph->left;
-    const int top = glyph->top;
-
-    const uint8_t* bitmap = &font.getData(style)->bitmap[offset];
-
-    if (bitmap != nullptr) {
-      for (int glyphY = 0; glyphY < height; glyphY++) {
-        for (int glyphX = 0; glyphX < width; glyphX++) {
-          const int pixelPosition = glyphY * width + glyphX;
-
-          // 90° counter-clockwise rotation transformation:
-          // screenX = mirrored CW X (right-to-left within advanceY span)
-          // screenY = yPos + (left + glyphX) (downward)
-          const int screenX = x + advanceY - 1 - (ascender - top + glyphY);
-          const int screenY = yPos + left + glyphX;
-
-          if (is2Bit) {
-            const uint8_t byte = bitmap[pixelPosition / 4];
-            const uint8_t bit_index = (3 - pixelPosition % 4) * 2;
-            const uint8_t bmpVal = 3 - (byte >> bit_index) & 0x3;
-
-            if (renderMode == BW && bmpVal < 3) {
-              drawPixel(screenX, screenY, black);
-            } else if (renderMode == GRAYSCALE_MSB && (bmpVal == 1 || bmpVal == 2)) {
-              drawPixel(screenX, screenY, false);
-            } else if (renderMode == GRAYSCALE_LSB && bmpVal == 1) {
-              drawPixel(screenX, screenY, false);
-            }
-          } else {
-            const uint8_t byte = bitmap[pixelPosition / 8];
-            const uint8_t bit_index = 7 - (pixelPosition % 8);
-
-            if ((byte >> bit_index) & 1) {
-              drawPixel(screenX, screenY, black);
-            }
-          }
-        }
-      }
-    }
-
-    // Move to next character position (going down, so increase Y)
-    yPos += glyph->advanceX;
   }
 }
 
@@ -1097,7 +1108,7 @@ bool GfxRenderer::storeBwBuffer() {
  * Uses chunked restoration to match chunked storage.
  */
 void GfxRenderer::restoreBwBuffer() {
-  // Check if any all chunks are allocated
+  // Check if all chunks are allocated
   bool missingChunks = false;
   for (const auto& bwBufferChunk : bwBufferChunks) {
     if (!bwBufferChunk) {
@@ -1112,13 +1123,6 @@ void GfxRenderer::restoreBwBuffer() {
   }
 
   for (size_t i = 0; i < BW_BUFFER_NUM_CHUNKS; i++) {
-    // Check if chunk is missing
-    if (!bwBufferChunks[i]) {
-      LOG_ERR("GFX", "!! BW buffer chunks not stored - this is likely a bug");
-      freeBwBufferChunks();
-      return;
-    }
-
     const size_t offset = i * BW_BUFFER_CHUNK_SIZE;
     memcpy(frameBuffer + offset, bwBufferChunks[i], BW_BUFFER_CHUNK_SIZE);
   }
@@ -1139,66 +1143,9 @@ void GfxRenderer::cleanupGrayscaleWithFrameBuffer() const {
   }
 }
 
-void GfxRenderer::renderChar(const EpdFontFamily& fontFamily, const uint32_t cp, int* x, const int* y,
+void GfxRenderer::renderChar(const EpdFontFamily& fontFamily, uint32_t cp, int* x, int* y, bool pixelState,
-                             const bool pixelState, const EpdFontFamily::Style style) const {
+                             EpdFontFamily::Style style) const {
-  const EpdGlyph* glyph = fontFamily.getGlyph(cp, style);
+  renderCharImpl<TextRotation::None>(*this, renderMode, fontFamily, cp, x, y, pixelState, style);
-  if (!glyph) {
-    glyph = fontFamily.getGlyph(REPLACEMENT_GLYPH, style);
-  }
-
-  // no glyph?
-  if (!glyph) {
-    LOG_ERR("GFX", "No glyph for codepoint %d", cp);
-    return;
-  }
-
-  const EpdFontData* fontData = fontFamily.getData(style);
-  const int is2Bit = fontData->is2Bit;
-  const uint8_t width = glyph->width;
-  const uint8_t height = glyph->height;
-  const int left = glyph->left;
-
-  const uint8_t* bitmap = getGlyphBitmap(fontData, glyph);
-
-  if (bitmap != nullptr) {
-    for (int glyphY = 0; glyphY < height; glyphY++) {
-      const int screenY = *y - glyph->top + glyphY;
-      for (int glyphX = 0; glyphX < width; glyphX++) {
-        const int pixelPosition = glyphY * width + glyphX;
-        const int screenX = *x + left + glyphX;
-
-        if (is2Bit) {
-          const uint8_t byte = bitmap[pixelPosition / 4];
-          const uint8_t bit_index = (3 - pixelPosition % 4) * 2;
-          // the direct bit from the font is 0 -> white, 1 -> light gray, 2 -> dark gray, 3 -> black
-          // we swap this to better match the way images and screen think about colors:
-          // 0 -> black, 1 -> dark grey, 2 -> light grey, 3 -> white
-          const uint8_t bmpVal = 3 - (byte >> bit_index) & 0x3;
-
-          if (renderMode == BW && bmpVal < 3) {
-            // Black (also paints over the grays in BW mode)
-            drawPixel(screenX, screenY, pixelState);
-          } else if (renderMode == GRAYSCALE_MSB && (bmpVal == 1 || bmpVal == 2)) {
-            // Light gray (also mark the MSB if it's going to be a dark gray too)
-            // We have to flag pixels in reverse for the gray buffers, as 0 leave alone, 1 update
-            drawPixel(screenX, screenY, false);
-          } else if (renderMode == GRAYSCALE_LSB && bmpVal == 1) {
-            // Dark gray
-            drawPixel(screenX, screenY, false);
-          }
-        } else {
-          const uint8_t byte = bitmap[pixelPosition / 8];
-          const uint8_t bit_index = 7 - (pixelPosition % 8);
-
-          if ((byte >> bit_index) & 1) {
-            drawPixel(screenX, screenY, pixelState);
-          }
-        }
-      }
-    }
-  }
-
-  *x += glyph->advanceX;
 }
 
 void GfxRenderer::getOrientedViewableTRBL(int* outTop, int* outRight, int* outBottom, int* outLeft) const {

lib/GfxRenderer/GfxRenderer.h

@@ -38,10 +38,9 @@ class GfxRenderer {
   uint8_t* bwBufferChunks[BW_BUFFER_NUM_CHUNKS] = {nullptr};
   std::map<int, EpdFontFamily> fontMap;
   FontDecompressor* fontDecompressor = nullptr;
-  void renderChar(const EpdFontFamily& fontFamily, uint32_t cp, int* x, const int* y, bool pixelState,
+  void renderChar(const EpdFontFamily& fontFamily, uint32_t cp, int* x, int* y, bool pixelState,
                   EpdFontFamily::Style style) const;
   void freeBwBufferChunks();
-  const uint8_t* getGlyphBitmap(const EpdFontData* fontData, const EpdGlyph* glyph) const;
   template <Color color>
   void drawPixelDither(int x, int y) const;
   template <Color color>
@@ -136,6 +135,9 @@ class GfxRenderer {
   void restoreBwBuffer();  // Restore and free the stored buffer
   void cleanupGrayscaleWithFrameBuffer() const;
 
+  // Font helpers
+  const uint8_t* getGlyphBitmap(const EpdFontData* fontData, const EpdGlyph* glyph) const;
+
   // Low level functions
   uint8_t* getFrameBuffer() const;
   static size_t getBufferSize();