Function avifEncoderCreateBitDepthExtensionItems

src/write.c:1293–1369

}

static avifResult avifEncoderCreateBitDepthExtensionItems(avifEncoder * encoder,
                                                          uint32_t gridCols,
                                                          uint32_t gridRows,
                                                          uint32_t gridWidth,
                                                          uint32_t gridHeight,
                                                          uint16_t colorItemID)
{
    AVIF_ASSERT_OR_RETURN(encoder->sampleTransformRecipe == AVIF_SAMPLE_TRANSFORM_BIT_DEPTH_EXTENSION_8B_8B ||
                          encoder->sampleTransformRecipe == AVIF_SAMPLE_TRANSFORM_BIT_DEPTH_EXTENSION_12B_4B ||
                          encoder->sampleTransformRecipe == AVIF_SAMPLE_TRANSFORM_BIT_DEPTH_EXTENSION_12B_8B_OVERLAP_4B);

    // There are multiple possible ISOBMFF box hierarchies for translucent images,
    // using 'sato' (Sample Transform) derived image items:
    //  - a primary 'sato' item uses a main color coded item and a hidden color coded item; each color coded
    //    item has an auxiliary alpha coded item; the main color coded item and the 'sato' item are in
    //    an 'altr' group (backward-compatible, implemented)
    //  - a primary 'sato' item uses a main color coded item and a hidden color coded item; the primary
    //    'sato' item has an auxiliary alpha 'sato' item using two alpha coded items (backward-incompatible)
    // Likewise, there are multiple possible ISOBMFF box hierarchies for bit-depth-extended grids,
    // using 'sato' (Sample Transform) derived image items:
    //  - a primary color 'grid', an auxiliary alpha 'grid', a hidden color 'grid', a hidden auxiliary alpha 'grid'
    //    and a 'sato' using the two color 'grid's as input items in this order; the primary color item
    //    and the 'sato' item being in an 'altr' group (backward-compatible, implemented)
    //  - a primary 'grid' of 'sato' cells and an auxiliary alpha 'grid' of 'sato' cells (backward-incompatible)
    avifEncoderItem * sampleTransformItem = avifEncoderDataCreateItem(encoder->data,
                                                                      "sato",
                                                                      infeNameSampleTransform,
                                                                      /*infeNameSize=*/strlen(infeNameSampleTransform) + 1,
                                                                      /*cellIndex=*/0);
    AVIF_CHECKRES(avifEncoderWriteSampleTransformPayload(encoder, &sampleTransformItem->metadataPayload));
    sampleTransformItem->itemCategory = AVIF_ITEM_SAMPLE_TRANSFORM;
    uint16_t sampleTransformItemID = sampleTransformItem->id;
    // 'altr' group
    AVIF_ASSERT_OR_RETURN(encoder->data->alternativeItemIDs.count == 0);
    uint16_t * alternativeItemID = (uint16_t *)avifArrayPush(&encoder->data->alternativeItemIDs);
    AVIF_CHECKERR(alternativeItemID != NULL, AVIF_RESULT_OUT_OF_MEMORY);
    *alternativeItemID = sampleTransformItem->id;
    alternativeItemID = (uint16_t *)avifArrayPush(&encoder->data->alternativeItemIDs);
    AVIF_CHECKERR(alternativeItemID != NULL, AVIF_RESULT_OUT_OF_MEMORY);
    *alternativeItemID = colorItemID;

    uint16_t bitDepthExtensionColorItemId;
    AVIF_CHECKRES(
        avifEncoderAddImageItems(encoder, gridCols, gridRows, gridWidth, gridHeight, AVIF_ITEM_SAMPLE_TRANSFORM_INPUT_0_COLOR, &bitDepthExtensionColorItemId));
    avifEncoderItem * bitDepthExtensionColorItem = avifEncoderDataFindItemByID(encoder->data, bitDepthExtensionColorItemId);
    assert(bitDepthExtensionColorItem);
    bitDepthExtensionColorItem->hiddenImage = AVIF_TRUE;

    // Set the color and bit depth extension items' dimgFromID value to point to the sample transform item.
    // The color item shall be first, and the bit depth extension item second. avifEncoderFinish() writes the
    // dimg item references in item id order, so as long as colorItemID < bitDepthExtensionColorItemId, the order
    // will be correct.
    AVIF_ASSERT_OR_RETURN(colorItemID < bitDepthExtensionColorItemId);
    avifEncoderItem * colorItem = avifEncoderDataFindItemByID(encoder->data, colorItemID);
    AVIF_ASSERT_OR_RETURN(colorItem != NULL);
    AVIF_ASSERT_OR_RETURN(colorItem->dimgFromID == 0); // The internal API only allows one dimg value per item.
    colorItem->dimgFromID = sampleTransformItemID;
    bitDepthExtensionColorItem->dimgFromID = sampleTransformItemID;