Allow to specify base font size (#3)

avvertix · web-flow · commit 463a724206c5 · 2026-04-30T09:13:16.000+02:00
diff --git a/README.md b/README.md
@@ -32,7 +32,7 @@ composer require avvertix/html-shot
 
 **Requirements**
 
-- PHP 8.1 or higher
+- PHP 8.2 or higher
 - FFI extension enabled `ext-ffi` | enabled (`ffi.enable = true` in `php.ini`) |
 
 
diff --git a/include/takumi_php.h b/include/takumi_php.h
@@ -112,6 +112,8 @@ void takumi_output_free(struct OutputHandle *handle);
  *   layout still happens at the logical dimensions.  Pass 0.0 to use 1.0.
  * - `format`: output format string "png" | "webp" | "jpeg" (null = "png")
  * - `quality`: JPEG/WebP quality 1–100 (0 = library default)
+ * - `base_font_size`: root font size in pixels used for `rem` and initial `em` resolution.
+ *   Pass 0.0 to use the default (16 px, matching the browser default).
  *
  * Returns an `OutputHandle` on success, or null on error.
  * The caller must free the handle with `takumi_output_free`.
@@ -124,6 +126,7 @@ struct OutputHandle *takumi_render_html(const struct ContextHandle *ctx,
                                         uint32_t height,
                                         float device_pixel_ratio,
                                         const char *format,
-                                        uint8_t quality);
+                                        uint8_t quality,
+                                        float base_font_size);
 
 #endif /* TAKUMI_PHP_H */
diff --git a/rust/src/ffi/render.rs b/rust/src/ffi/render.rs
@@ -25,6 +25,8 @@ use crate::error::set_last_error;
 ///   layout still happens at the logical dimensions.  Pass 0.0 to use 1.0.
 /// - `format`: output format string "png" | "webp" | "jpeg" (null = "png")
 /// - `quality`: JPEG/WebP quality 1–100 (0 = library default)
+/// - `base_font_size`: root font size in pixels used for `rem` and initial `em` resolution.
+///   Pass 0.0 to use the default (16 px, matching the browser default).
 ///
 /// Returns an `OutputHandle` on success, or null on error.
 /// The caller must free the handle with `takumi_output_free`.
@@ -39,6 +41,7 @@ pub unsafe extern "C" fn takumi_render_html(
     device_pixel_ratio: f32,
     format: *const c_char,
     quality: u8,
+    base_font_size: f32,
 ) -> *mut OutputHandle {
     if ctx.is_null() || html.is_null() {
         set_last_error("null pointer: ctx or html");
@@ -93,8 +96,12 @@ pub unsafe extern "C" fn takumi_render_html(
 
     // Render
     let dpr = if device_pixel_ratio > 0.0 { device_pixel_ratio } else { 1.0 };
+    let mut viewport = Viewport::new((width, height)).with_device_pixel_ratio(dpr);
+    if base_font_size > 0.0 {
+        viewport = viewport.with_font_size(base_font_size);
+    }
     let render_options = takumi::rendering::RenderOptions::builder()
-        .viewport(Viewport::new((width, height)).with_device_pixel_ratio(dpr))
+        .viewport(viewport)
         .node(root_node)
         .global(&ctx_data.global)
         .stylesheet(stylesheet)
diff --git a/src/HtmlShot/Renderer.php b/src/HtmlShot/Renderer.php
@@ -35,6 +35,8 @@ public function __construct(
      * @param  float  $devicePixelRatio  Output scale factor: 1.0 = normal, 2.0 = HiDPI/Retina.
      *                                   Layout stays at $width×$height logical px; the output bitmap
      *                                   is ($width * dpr) × ($height * dpr) physical pixels.
+     * @param  float  $baseFontSize  Root font size in pixels for `rem` and initial `em` resolution.
+     *                               Matches the browser's `<html>` font-size. Default is 16 px.
      * @return string Raw image bytes.
      *
      * @throws Exception\RuntimeException on render failure.
@@ -47,6 +49,7 @@ public function render(
         int $quality = 0,
         array $stylesheets = [],
         float $devicePixelRatio = 1.0,
+        float $baseFontSize = 16.0,
     ): string {
         $ffi = TakumiFfi::instance();
 
@@ -67,6 +70,7 @@ public function render(
             (float) $devicePixelRatio,
             TakumiFfi::cstring($format),
             $quality,
+            $baseFontSize,
         );
 
         // $cssBufs must stay in scope until the FFI call returns
diff --git a/src/HtmlShot/TakumiFfi.php b/src/HtmlShot/TakumiFfi.php
@@ -22,7 +22,7 @@
  * @method int takumi_output_size(CData $handle)
  * @method int takumi_output_save(CData $handle, CData $path)
  * @method void takumi_output_free(CData $handle)
- * @method ?CData takumi_render_html(CData $ctx, CData $html, ?CData $stylesheets, int $stylesheets_len, int $width, int $height, float $device_pixel_ratio, CData $format, int $quality)
+ * @method ?CData takumi_render_html(CData $ctx, CData $html, ?CData $stylesheets, int $stylesheets_len, int $width, int $height, float $device_pixel_ratio, CData $format, int $quality, float $base_font_size)
  * @method ?CData new(string $type, bool $owned = true, bool $persistent = false)
  */
 final class TakumiFfi
