Merge pull request #238 from 0xbe7a/init-forms-options

add option for opt-in form rendering

Author: bobsingor

.changeset/weak-pugs-hear.md

@@ -0,0 +1,25 @@
+---
+'@embedpdf/engines': minor
+'@embedpdf/models': minor
+'@embedpdf/plugin-render': minor
+---
+
+Add optional **form widget rendering** to the render pipeline.
+
+### What changed
+
+- **@embedpdf/models**
+
+  - `PdfRenderPageOptions` now supports `withForms?: boolean` to request drawing interactive form widgets.
+
+- **@embedpdf/engines**
+
+  - `PdfiumEngine.renderPage` and `renderPageRect` honor `withForms`.  
+    When enabled, the engine initializes the page form handle and calls `FPDF_FFLDraw` with the correct device transform.
+  - New helper `computeFormDrawParams(matrix, rect, pageSize, rotation)` calculates start offsets and sizes for `FPDF_FFLDraw`.
+
+- **@embedpdf/plugin-render**
+  - New plugin config flags:
+    - `withForms?: boolean` (default `false`)
+    - `withAnnotations?: boolean` (default `false`)
+  - The plugin merges per-call options with plugin defaults so callers can set once at init or override per call.

packages/engines/src/lib/pdfium/engine.ts

@@ -24,6 +24,7 @@ import {
   PdfWidgetAnnoOption,
   PdfFileAttachmentAnnoObject,
   Rect,
+  Size,
   PdfAttachmentObject,
   PdfUnsupportedAnnoObject,
   PdfTextAnnoObject,
@@ -114,13 +115,14 @@ import {
   PdfAnnotationsProgress,
   ConvertToBlobOptions,
   buildUserToDeviceMatrix,
+  Matrix,
   PdfMetadataObject,
   PdfPrintOptions,
   PdfTrappedStatus,
   PdfStampFit,
   PdfAddAttachmentParams,
 } from '@embedpdf/models';
-import { isValidCustomKey, readArrayBuffer, readString } from './helper';
+import { computeFormDrawParams, isValidCustomKey, readArrayBuffer, readString } from './helper';
 import { WrappedPdfiumModule } from '@embedpdf/pdfium';
 import { DocumentContext, PageContext, PdfCache } from './cache';
 import { ImageDataConverter, LazyImageData } from '../converters/types';
@@ -6956,6 +6958,8 @@ export class PdfiumEngine<T = Blob> implements PdfEngine<T> {
     const bytes = stride * hDev;
 
     const pageCtx = ctx.acquirePage(page.index);
+    const shouldRenderForms = options?.withForms ?? false;
+    const formHandle = shouldRenderForms ? pageCtx.getFormHandle() : undefined;
 
     // ---- 2) allocate a BGRA bitmap in WASM
     const heapPtr = this.memoryManager.malloc(bytes);
@@ -6992,6 +6996,24 @@ export class PdfiumEngine<T = Blob> implements PdfEngine<T> {
         clipPtr,
         flags,
       );
+
+      if (formHandle !== undefined) {
+        const formParams = computeFormDrawParams(M, rect, page.size, rotation);
+        const { startX, startY, formsWidth, formsHeight, scaleX, scaleY } = formParams;
+
+        // Draw form elements using the same effective transform as the page bitmap.
+        this.pdfiumModule.FPDF_FFLDraw(
+          formHandle,
+          bitmapPtr,
+          pageCtx.pagePtr,
+          startX,
+          startY,
+          formsWidth,
+          formsHeight,
+          rotation,
+          flags,
+        );
+      }
     } finally {
       pageCtx.release();
       this.memoryManager.free(mPtr);

packages/engines/src/lib/pdfium/helper.ts

@@ -1,3 +1,4 @@
+import { Matrix, Rotation, Rect, Size } from '@embedpdf/models';
 import { PdfiumRuntimeMethods, PdfiumModule } from '@embedpdf/pdfium';
 
 /**
@@ -92,3 +93,65 @@ export function isValidCustomKey(key: string): boolean {
   }
   return true;
 }
+
+interface FormDrawParams {
+  startX: number;
+  startY: number;
+  formsWidth: number;
+  formsHeight: number;
+  scaleX: number;
+  scaleY: number;
+}
+
+export function computeFormDrawParams(
+  matrix: Matrix,
+  rect: Rect,
+  pageSize: Size,
+  rotation: Rotation,
+): FormDrawParams {
+  const rectLeft = rect.origin.x;
+  const rectBottom = rect.origin.y;
+  const rectRight = rectLeft + rect.size.width;
+  const rectTop = rectBottom + rect.size.height;
+  const pageWidth = pageSize.width;
+  const pageHeight = pageSize.height;
+
+  // Extract the per-axis scale that the render matrix applies.
+  const scaleX = Math.hypot(matrix.a, matrix.b);
+  const scaleY = Math.hypot(matrix.c, matrix.d);
+  const swap = (rotation & 1) === 1;
+
+  const formsWidth = swap
+    ? Math.max(1, Math.round(pageHeight * scaleX))
+    : Math.max(1, Math.round(pageWidth * scaleX));
+  const formsHeight = swap
+    ? Math.max(1, Math.round(pageWidth * scaleY))
+    : Math.max(1, Math.round(pageHeight * scaleY));
+
+  let startX: number;
+  let startY: number;
+  switch (rotation) {
+    case Rotation.Degree0:
+      startX = -Math.round(rectLeft * scaleX);
+      startY = -Math.round(rectBottom * scaleY);
+      break;
+    case Rotation.Degree90:
+      startX = Math.round((rectTop - pageHeight) * scaleX);
+      startY = -Math.round(rectLeft * scaleY);
+      break;
+    case Rotation.Degree180:
+      startX = Math.round((rectRight - pageWidth) * scaleX);
+      startY = Math.round((rectTop - pageHeight) * scaleY);
+      break;
+    case Rotation.Degree270:
+      startX = -Math.round(rectBottom * scaleX);
+      startY = Math.round((rectRight - pageWidth) * scaleY);
+      break;
+    default:
+      startX = -Math.round(rectLeft * scaleX);
+      startY = -Math.round(rectBottom * scaleY);
+      break;
+  }
+
+  return { startX, startY, formsWidth, formsHeight, scaleX, scaleY };
+}

packages/models/src/pdf.ts

@@ -2512,6 +2512,10 @@ export interface PdfRenderPageOptions extends PdfRenderOptions {
    * Whether to render annotations
    */
   withAnnotations?: boolean;
+  /**
+   * Whether to render interactive form widgets
+   */
+  withForms?: boolean;
 }
 
 export interface PdfRenderPageAnnotationOptions extends PdfRenderOptions {

packages/plugin-render/src/lib/render-plugin.ts

@@ -16,6 +16,8 @@ export class RenderPlugin extends BasePlugin<RenderPluginConfig, RenderCapabilit
   static readonly id = 'render' as const;
 
   private readonly refreshPages$ = createEmitter<number[]>();
+  private withForms = false;
+  private withAnnotations = false;
 
   constructor(id: string, registry: PluginRegistry) {
     super(id, registry);
@@ -25,7 +27,10 @@ export class RenderPlugin extends BasePlugin<RenderPluginConfig, RenderCapabilit
     });
   }
 
-  async initialize(_config: RenderPluginConfig): Promise<void> {}
+  async initialize(config: RenderPluginConfig): Promise<void> {
+    this.withForms = config.withForms ?? false;
+    this.withAnnotations = config.withAnnotations ?? false;
+  }
 
   protected buildCapability(): RenderCapability {
     return {
@@ -50,7 +55,13 @@ export class RenderPlugin extends BasePlugin<RenderPluginConfig, RenderCapabilit
       throw new Error('page does not exist');
     }
 
-    return this.engine.renderPage(coreState.document, page, options);
+    const mergedOptions = {
+      ...(options ?? {}),
+      withForms: options?.withForms ?? this.withForms,
+      withAnnotations: options?.withAnnotations ?? this.withAnnotations,
+    };
+
+    return this.engine.renderPage(coreState.document, page, mergedOptions);
   }
 
   private renderPageRect({ pageIndex, rect, options }: RenderPageRectOptions) {
@@ -65,6 +76,12 @@ export class RenderPlugin extends BasePlugin<RenderPluginConfig, RenderCapabilit
       throw new Error('page does not exist');
     }
 
-    return this.engine.renderPageRect(coreState.document, page, rect, options);
+    const mergedOptions = {
+      ...(options ?? {}),
+      withForms: options?.withForms ?? this.withForms,
+      withAnnotations: options?.withAnnotations ?? this.withAnnotations,
+    };
+
+    return this.engine.renderPageRect(coreState.document, page, rect, mergedOptions);
   }
 }

packages/plugin-render/src/lib/types.ts

@@ -1,7 +1,18 @@
 import { BasePluginConfig } from '@embedpdf/core';
 import { PdfErrorReason, PdfRenderPageOptions, Rect, Task } from '@embedpdf/models';
 
-export interface RenderPluginConfig extends BasePluginConfig {}
+export interface RenderPluginConfig extends BasePluginConfig {
+  /**
+   * Initialize and draw form widgets during renders.
+   * Defaults to `false`.
+   */
+  withForms?: boolean;
+  /**
+   * Whether to render annotations
+   * Defaults to `false`.
+   */
+  withAnnotations?: boolean;
+}
 
 export interface RenderPageRectOptions {
   pageIndex: number;