From 372e587ea8886c2f1c386d620d32e58e356ed6fd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sami=20Kalliom=C3=A4ki?= <sakal@webrtc.org>
Date: Tue, 27 Jun 2017 17:00:21 +0200
Subject: [PATCH] Fix samplingMatrix for I420Frames converted from VideoFrame.
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The conversion code was wrong because it assumed the 3x3 matrix is a
XYZ-matrix when it really is XYW-matrix. We have to override the matrix
for I420 frames to flip the vertically before rendering.

R=magjed@webrtc.org

Bug: webrtc:7760
Change-Id: I1f08c1a929bf5721706e2a902701100cf7a9c31d
Reviewed-on: https://chromium-review.googlesource.com/541346
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Commit-Queue: Sami Kalliomäki <sakal@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#18801}
---
 .../android/api/org/webrtc/VideoRenderer.java | 16 ++++++------
 .../sdk/android/src/jni/native_handle_impl.cc | 25 ++++++++++++++-----
 2 files changed, 27 insertions(+), 14 deletions(-)

diff --git a/webrtc/sdk/android/api/org/webrtc/VideoRenderer.java b/webrtc/sdk/android/api/org/webrtc/VideoRenderer.java
index 9dde095242..0825b7408b 100644
--- a/webrtc/sdk/android/api/org/webrtc/VideoRenderer.java
+++ b/webrtc/sdk/android/api/org/webrtc/VideoRenderer.java
@@ -61,13 +61,7 @@ public class VideoRenderer {
       // top-left corner of the image, but in glTexImage2D() the first element corresponds to the
       // bottom-left corner. This discrepancy is corrected by setting a vertical flip as sampling
       // matrix.
-      // clang-format off
-      samplingMatrix = new float[] {
-          1,  0, 0, 0,
-          0, -1, 0, 0,
-          0,  0, 1, 0,
-          0,  1, 0, 1};
-      // clang-format on
+      samplingMatrix = RendererCommon.verticalFlipMatrix();
     }
 
     /**
@@ -100,11 +94,11 @@ public class VideoRenderer {
       if (rotationDegree % 90 != 0) {
         throw new IllegalArgumentException("Rotation degree not multiple of 90: " + rotationDegree);
       }
-      this.samplingMatrix = samplingMatrix;
       if (buffer instanceof VideoFrame.TextureBuffer) {
         VideoFrame.TextureBuffer textureBuffer = (VideoFrame.TextureBuffer) buffer;
         this.yuvFrame = false;
         this.textureId = textureBuffer.getTextureId();
+        this.samplingMatrix = samplingMatrix;
 
         this.yuvStrides = null;
         this.yuvPlanes = null;
@@ -115,6 +109,12 @@ public class VideoRenderer {
             new int[] {i420Buffer.getStrideY(), i420Buffer.getStrideU(), i420Buffer.getStrideV()};
         this.yuvPlanes =
             new ByteBuffer[] {i420Buffer.getDataY(), i420Buffer.getDataU(), i420Buffer.getDataV()};
+        // The convention in WebRTC is that the first element in a ByteBuffer corresponds to the
+        // top-left corner of the image, but in glTexImage2D() the first element corresponds to the
+        // bottom-left corner. This discrepancy is corrected by multiplying the sampling matrix with
+        // a vertical flip matrix.
+        this.samplingMatrix =
+            RendererCommon.multiplyMatrices(samplingMatrix, RendererCommon.verticalFlipMatrix());
 
         this.textureId = 0;
       }
diff --git a/webrtc/sdk/android/src/jni/native_handle_impl.cc b/webrtc/sdk/android/src/jni/native_handle_impl.cc
index 907c90e092..ae4de0b3bc 100644
--- a/webrtc/sdk/android/src/jni/native_handle_impl.cc
+++ b/webrtc/sdk/android/src/jni/native_handle_impl.cc
@@ -43,12 +43,25 @@ Matrix Matrix::fromAndroidGraphicsMatrix(JNIEnv* jni, jobject j_matrix) {
   jfloat* array_3x3_ptr = jni->GetFloatArrayElements(array_3x3, nullptr);
   Matrix matrix;
   memset(matrix.elem_, 0, sizeof(matrix.elem_));
-  for (int y = 0; y < 3; ++y) {
-    for (int x = 0; x < 3; ++x) {
-      matrix.elem_[y * 4 + x] = array_3x3_ptr[x + y * 3];
-    }
-  }
-  matrix.elem_[3 + 3 * 3] = 1;  // Bottom-right corner should be 1.
+  // The android.graphics.Matrix looks like this:
+  // [x1 y1 w1]
+  // [x2 y2 w2]
+  // [x3 y3 w3]
+  // We want to contruct a matrix that looks like this:
+  // [x1 y1  0 w1]
+  // [x2 y2  0 w2]
+  // [ 0  0  1  0]
+  // [x3 y3  0 w3]
+  matrix.elem_[0 * 4 + 0] = array_3x3_ptr[0 * 3 + 0];
+  matrix.elem_[0 * 4 + 1] = array_3x3_ptr[0 * 3 + 1];
+  matrix.elem_[0 * 4 + 3] = array_3x3_ptr[0 * 3 + 2];
+  matrix.elem_[1 * 4 + 0] = array_3x3_ptr[1 * 3 + 0];
+  matrix.elem_[1 * 4 + 1] = array_3x3_ptr[1 * 3 + 1];
+  matrix.elem_[1 * 4 + 3] = array_3x3_ptr[1 * 3 + 2];
+  matrix.elem_[2 * 4 + 2] = 1;  // Z-scale should be 1.
+  matrix.elem_[3 * 4 + 0] = array_3x3_ptr[2 * 3 + 0];
+  matrix.elem_[3 * 4 + 1] = array_3x3_ptr[2 * 3 + 1];
+  matrix.elem_[3 * 4 + 3] = array_3x3_ptr[2 * 3 + 2];
   return matrix;
 }