pdf_to_jpeg.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// Standard JPEG library
#include <jpeglib.h>

// Your local PDFium headers
#include "pdfium/include/fpdfview.h"
#include "pdfium/include/fpdf_text.h"

// --- Helper: Save BGRx buffer to JPEG ---
// PDFium gives us BGRx (Blue-Green-Red-Alpha/Unused).
// LibJPEG expects RGB. We swap channels row-by-row here.
void save_jpeg(const char *filename, const unsigned char *buffer, int width, int height, int stride) {
    struct jpeg_compress_struct cinfo;
    struct jpeg_error_mgr jerr;
    FILE *outfile;

    cinfo.err = jpeg_std_error(&jerr);
    jpeg_create_compress(&cinfo);

    if ((outfile = fopen(filename, "wb")) == NULL) {
        fprintf(stderr, "Cannot open %s\n", filename);
        return;
    }
    jpeg_stdio_dest(&cinfo, outfile);

    cinfo.image_width = width;
    cinfo.image_height = height;
    cinfo.input_components = 4;   
    cinfo.in_color_space = JCS_EXT_BGRX; 

    printf("BEFORE jpeg_set_defaults:\n");
    printf("  in_color_space = %d\n", cinfo.in_color_space);
    printf("  input_components = %d\n", cinfo.input_components);

    jpeg_set_defaults(&cinfo);
    
    printf("AFTER jpeg_set_defaults:\n");
    printf("  in_color_space = %d\n", cinfo.in_color_space);
    printf("  input_components = %d\n", cinfo.input_components);
    printf("  jpeg_color_space = %d\n", cinfo.jpeg_color_space);
    printf("  num_components = %d\n", cinfo.num_components);

    jpeg_set_quality(&cinfo, 90, TRUE);
    
    printf("BEFORE jpeg_start_compress:\n");
    printf("  in_color_space = %d\n", cinfo.in_color_space);
    printf("  input_components = %d\n", cinfo.input_components);
    
    jpeg_start_compress(&cinfo, TRUE);

    JSAMPROW row_pointer[1];
    while (cinfo.next_scanline < cinfo.image_height) {
        row_pointer[0] = (JSAMPROW)(buffer + (cinfo.next_scanline * stride));
        jpeg_write_scanlines(&cinfo, row_pointer, 1);
    }

    jpeg_finish_compress(&cinfo);
    fclose(outfile);
    jpeg_destroy_compress(&cinfo);
    
    printf("Saved JPEG (Fast Mode) to %s\n", filename);
}

int main() {
    const char *input_file = "input.pdf";
    const char *output_image = "output.jpg";

    // --- INIT ---
    FPDF_LIBRARY_CONFIG config;
    memset(&config, 0, sizeof(config));
    config.version = 2;
    FPDF_InitLibraryWithConfig(&config);

    // --- LOAD ---
    FPDF_DOCUMENT doc = FPDF_LoadDocument(input_file, NULL);
    if (!doc) {
        fprintf(stderr, "Err: %lu\n", FPDF_GetLastError());
        return 1;
    }
    FPDF_PAGE page = FPDF_LoadPage(doc, 0);

    // 3. Calculate High-DPI Dimensions
    // FPDF_GetPageWidth returns "points" (1/72 inch)
    double pts_width = FPDF_GetPageWidth(page);
    double pts_height = FPDF_GetPageHeight(page);
    float scale = 2.0;

    int px_width = (int)(pts_width * scale);
    int px_height = (int)(pts_height * scale);

    // 4. Render
    FPDF_BITMAP bitmap = FPDFBitmap_Create(px_width, px_height, 0);
    FPDFBitmap_FillRect(bitmap, 0, 0, px_width, px_height, 0xFFFFFFFF);
    FPDF_RenderPageBitmap(bitmap, page, 0, 0, px_width, px_height, 0, 0);

    // 5. Save
    const unsigned char *buffer = (const unsigned char *)FPDFBitmap_GetBuffer(bitmap);
    int stride = FPDFBitmap_GetStride(bitmap);
    
    save_jpeg(output_image, buffer, px_width, px_height, stride);

    // --- CLEANUP ---
    FPDFBitmap_Destroy(bitmap);
    FPDF_ClosePage(page);
    FPDF_CloseDocument(doc);
    FPDF_DestroyLibrary();

    return 0;
}