Merge "ExternalCameraHAL: Pad AllocatedFrame by DCTSIZE" into main
diff --git a/camera/device/3.4/default/ExternalCameraUtils.cpp b/camera/device/3.4/default/ExternalCameraUtils.cpp
index 8f4626c..d9610c2 100644
--- a/camera/device/3.4/default/ExternalCameraUtils.cpp
+++ b/camera/device/3.4/default/ExternalCameraUtils.cpp
@@ -108,9 +108,38 @@
return -EINVAL;
}
- uint32_t dataSize = mWidth * mHeight * 3 / 2; // YUV420
- if (mData.size() != dataSize) {
- mData.resize(dataSize);
+ // This frame might be sent to jpeglib to be encoded. Since AllocatedFrame only contains YUV420,
+ // jpeglib expects height and width of Y component to be an integral multiple of 2*DCTSIZE,
+ // and heights and widths of Cb and Cr components to be an integral multiple of DCTSIZE. If the
+ // image size does not meet this requirement, libjpeg expects its input to be padded to meet the
+ // constraints. This padding is removed from the final encoded image so the content in the
+ // padding doesn't matter. What matters is that the memory is accessible to jpeglib at the time
+ // of encoding.
+ // For example, if the image size is 1500x844 and DCTSIZE is 8, jpeglib expects a YUV 420
+ // frame with components of following sizes:
+ // Y: 1504x848 because 1504 and 848 are the next smallest multiples of 2*8
+ // Cb/Cr: 752x424 which are the next smallest multiples of 8
+
+ // jpeglib takes an array of row pointers which makes vertical padding trivial when setting up
+ // the pointers. Padding horizontally is a bit more complicated. AllocatedFrame holds the data
+ // in a flattened buffer, which means memory accesses past a row will flow into the next logical
+ // row. For any row of a component, we can consider the first few bytes of the next row as
+ // padding for the current one. This is true for Y and Cb components and all but last row of the
+ // Cr component. Reading past the last row of Cr component will lead to undefined behavior as
+ // libjpeg attempts to read memory past the allocated buffer. To prevent undefined behavior,
+ // the buffer allocated here is padded such that libjpeg never accesses unallocated memory when
+ // reading the last row. Effectively, we only need to ensure that the last row of Cr component
+ // has width that is an integral multiple of DCTSIZE.
+
+ size_t dataSize = mWidth * mHeight * 3 / 2; // YUV420
+
+ size_t cbWidth = mWidth / 2;
+ size_t requiredCbWidth = DCTSIZE * ((cbWidth + DCTSIZE - 1) / DCTSIZE);
+ size_t padding = requiredCbWidth - cbWidth;
+ size_t finalSize = dataSize + padding;
+
+ if (mData.size() != finalSize) {
+ mData.resize(finalSize);
}
if (out != nullptr) {