android-ndk - libpng を使用して画像を読み込むと、予期しないピクセルデータが生成される

Question

アプリケーションに png ファイルをロードしようとすると問題が発生します。ヘッダーを正常にロードし、画像がpngであることを認識しているようですが、画像は実際には単色ではありませんが、何らかの理由で出力に同じ値があります。私を悩ませているもう 1 つのことは、16 バイトが未読のままになっていることです。

私のコード:

AAsset* pngAsset_ = 0;
AAssetManager* pngAassetManager_ = 0;

void png_asset_read(png_structp png, png_bytep data, png_size_t size) {
    //AAsset_seek(pngAsset_, 0, 0);
    AAsset_read(pngAsset_, data, size);
    int numBytesRemaining = AAsset_getRemainingLength(pngAsset_);
    LOGI("Read size: %d, remaining: %d", size, numBytesRemaining);
}

Image* loadPngFile(AAssetManager* assetManager) {
    pngAassetManager_ = assetManager;

    LOGI("Trying to load image...");
    int HEADER_SIZE = 8;
    string filename = "skybox.png";
    pngAsset_ = AAssetManager_open(pngAassetManager_, filename.c_str(),
            AASSET_MODE_UNKNOWN);
    if (pngAsset_ == 0) {
        LOGW("Asset \"%s\" not found.", filename.c_str());
        return 0;
    }

    off_t bufferSize = AAsset_getLength(pngAsset_);
    png_byte* buffer = new png_byte[HEADER_SIZE];

    int numBytesRead = AAsset_read(pngAsset_, buffer, HEADER_SIZE);
    int numBytesRemaining = AAsset_getRemainingLength(pngAsset_);

    int is_png = !png_sig_cmp(buffer, 0, 8);
    if (!is_png) {
        LOGE("File %s format is not PNG.", filename.c_str());
        return 0;
    }
    LOGI("Size of the file: %d, bytes read: %d, bytes remain: %d",
            bufferSize, numBytesRead, numBytesRemaining);

    png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL,
            NULL, NULL);
    if (!png_ptr) {
        LOGE("Unable to create PNG structure: %s", filename.c_str());
        return 0;
    }

    png_infop info_ptr = png_create_info_struct(png_ptr);
    if (!info_ptr) {
        png_destroy_read_struct(&png_ptr, (png_infopp) NULL, (png_infopp) NULL);
        LOGE("Unable to create png info : %s", filename.c_str());
        return 0;
    }

    png_infop end_info = png_create_info_struct(png_ptr);
    if (!end_info) {
        png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp) NULL);
        LOGE("Unable to create png end info : %s", filename.c_str());
        return 0;
    }

    if (setjmp(png_jmpbuf(png_ptr))) {
        LOGE("Error during setjmp : %s", filename.c_str());
        png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
        return 0;
    }
    png_set_read_fn(png_ptr, NULL, png_asset_read);
    png_set_sig_bytes(png_ptr, 8);
    png_read_info(png_ptr, info_ptr);

    int bit_depth, color_type;
    png_uint_32 twidth, theight;
    png_get_IHDR(png_ptr, info_ptr, &twidth, &theight, &bit_depth, &color_type,
            NULL, NULL, NULL);
    LOGI("Width: %d, height: %d.", twidth, theight);

    // Update the png info struct.
    png_read_update_info(png_ptr, info_ptr);

    // Row size in bytes.
    int rowbytes = png_get_rowbytes(png_ptr, info_ptr);
    LOGI("Row size: %d bytes.", rowbytes);

    // Allocate the image_data as a big block, to be given to opengl
    png_byte *image_data = new png_byte[rowbytes * theight];
    if (!image_data) {
        //clean up memory and close stuff
        png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
        LOGE(
                "Unable to allocate image_data while loading %s ", filename.c_str());
    }

    //row_pointers is for pointing to image_data for reading the png with libpng
    png_bytep *row_pointers = new png_bytep[theight];
    if (!row_pointers) {
        //clean up memory and close stuff
        png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
        delete[] image_data;
        LOGE(
                "Unable to allocate row_pointer while loading %s ", filename.c_str());
    }
    // set the individual row_pointers to point at the correct offsets of image_data
    for (int i = 0; i < theight; ++i)
        row_pointers[theight - 1 - i] = image_data + i * rowbytes;

    //read the png into image_data through row_pointers
    png_read_image(png_ptr, row_pointers);

    for (int i = 0; i < 10; i ++) {
        LOGI("Pixel %d: %f %f %f %f",i, image_data[i * 4], image_data[i * 4 + 1],
                image_data[i * 4 + 2], image_data[i * 4 + 3]);
    }

    //Now generate the OpenGL texture object
    Image* image = new Image((unsigned char*) image_data, twidth, theight,
            twidth * theight * 4, 0);

    png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
    delete[] row_pointers;

    AAsset_close(pngAsset_);

    return image;
}

出力：

06-30 23:49:00.651: I/Ghost Engine(21279): Trying to load image...
06-30 23:49:00.651: I/Ghost Engine(21279): Size of the file: 529452, bytes read: 8, bytes remain: 529444
06-30 23:49:00.651: I/Ghost Engine(21279): Read size: 8, remaining: 529436
06-30 23:49:00.651: I/Ghost Engine(21279): Read size: 13, remaining: 529423
06-30 23:49:00.651: I/Ghost Engine(21279): Read size: 4, remaining: 529419
06-30 23:49:00.651: I/Ghost Engine(21279): Read size: 8, remaining: 529411
06-30 23:49:00.651: I/Ghost Engine(21279): Read size: 9, remaining: 529402
06-30 23:49:00.651: I/Ghost Engine(21279): Read size: 4, remaining: 529398
06-30 23:49:00.651: I/Ghost Engine(21279): Read size: 8, remaining: 529390
06-30 23:49:00.651: I/Ghost Engine(21279): Read size: 32, remaining: 529358
06-30 23:49:00.651: I/Ghost Engine(21279): Read size: 4, remaining: 529354
06-30 23:49:00.651: I/Ghost Engine(21279): Read size: 8, remaining: 529346
06-30 23:49:00.651: I/Ghost Engine(21279): Width: 1024, height: 1024.
06-30 23:49:00.651: I/Ghost Engine(21279): Row size: 4096 bytes.
06-30 23:49:00.651: I/Ghost Engine(21279): Read size: 8192, remaining: 521154
06-30 23:49:00.681: I/Ghost Engine(21279): Read size: 8192, remaining: 512962
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06-30 23:49:00.851: I/Ghost Engine(21279): Read size: 5042, remaining: 16
06-30 23:49:00.861: I/Ghost Engine(21279): Pixel 0: 0.000000 0.000000 1197.166992 1420.242434
06-30 23:49:00.861: I/Ghost Engine(21279): Pixel 1: 0.000000 0.000000 1197.166992 1420.242434
06-30 23:49:00.861: I/Ghost Engine(21279): Pixel 2: 0.000000 0.000000 1197.166992 1420.242434
06-30 23:49:00.861: I/Ghost Engine(21279): Pixel 3: 0.000000 0.000000 1197.166992 1420.242434
06-30 23:49:00.861: I/Ghost Engine(21279): Pixel 4: 0.000000 0.000000 1197.166992 1420.242434
06-30 23:49:00.861: I/Ghost Engine(21279): Pixel 5: 0.000000 0.000000 1197.166992 1420.242434
06-30 23:49:00.861: I/Ghost Engine(21279): Pixel 6: 0.000000 0.000000 1197.166992 1420.242434
06-30 23:49:00.861: I/Ghost Engine(21279): Pixel 7: 0.000000 0.000000 1197.166992 1420.242434
06-30 23:49:00.861: I/Ghost Engine(21279): Pixel 8: 0.000000 0.000000 1197.166992 1420.242434
06-30 23:49:00.861: I/Ghost Engine(21279): Pixel 9: 0.000000 0.000000 1197.166992 1420.242434
06-30 23:49:00.871: I/Ghost Engine(21279): Image id: 1.
06-30 23:49:00.871: I/Ghost Engine(21279): Image dimensions: 1024 x 1024
06-30 23:49:00.871: I/Ghost Engine(21279): Image size: 4194304

すべてがうまくいかなくなる可能性があるアイデアはありますか? ありがとう、マーティン。

score 0 · Accepted Answer

問題が見つかりました:

"Pixel %d: %f %f %f %f"

になるはずだった：

"Pixel %d: %d %d %d %d"

どうやら画像は正常に読み込まれているようです。

android-ndk - libpng を使用して画像を読み込むと、予期しないピクセル データが生成される

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android-ndk - libpng を使用して画像を読み込むと、予期しないピクセルデータが生成される