提升 Android SDK (Kotlin/Java) 上的相機圖片穩定性

ARCore 現在支援電子圖像穩定技術 (EIS)，有助於產生流暢的相機預覽畫面。EIS 透過陀螺儀觀察手機動作，並在相機紋理邊界內套用補償形態網格，藉此抵禦未成年人搖晃，讓手機穩定運作。裝置螢幕的直向模式才支援 EIS。ARCore 1.39.0 版支援所有方向。

查詢 EIS 支援並啟用 EIS

如要啟用 EIS，請將工作階段設為使用「ImageStabilizationMode.EIS」。如果裝置不支援 EIS 功能，將會導致 ARCore 擲回例外狀況。

Java

if (!session.isImageStabilizationModeSupported(Config.ImageStabilizationMode.EIS)) {
  return;
}
Config config = session.getConfig();
config.setImageStabilizationMode(Config.ImageStabilizationMode.EIS);
session.configure(config);

Kotlin

if (!session.isImageStabilizationModeSupported(Config.ImageStabilizationMode.EIS)) return
session.configure(
  session.config.apply { imageStabilizationMode = Config.ImageStabilizationMode.EIS }
)

轉換座標

開啟 EIS 時，轉譯器必須使用修改過的裝置座標，以及算繪相機背景時加入 EIS 補償的紋理座標。如要取得 EIS 補償座標，請使用 Frame.transformCoordinates3d()，將 OPENGL_NORMALIZED_DEVICE_COORDINATES 做為輸入內容，並使用 EIS_NORMALIZED_DEVICE_COORDINATES 做為輸出內容，取得 3D 裝置座標，並使用 EIS_TEXTURE_NORMALIZED 做為輸出內容，取得 3D 紋理座標。目前，Frame.transformCoordinates3d() 唯一支援的輸入座標類型是 OPENGL_NORMALIZED_DEVICE_COORDINATES。

Java

final FloatBuffer cameraTexCoords =
    ByteBuffer.allocateDirect(COORDS_BUFFER_SIZE_3D)
        .order(ByteOrder.nativeOrder())
        .asFloatBuffer();

final FloatBuffer screenCoords =
    ByteBuffer.allocateDirect(COORDS_BUFFER_SIZE_3D)
        .order(ByteOrder.nativeOrder())
        .asFloatBuffer();

final FloatBuffer NDC_QUAD_COORDS_BUFFER =
    ByteBuffer.allocateDirect(COORDS_BUFFER_SIZE_2D)
        .order(ByteOrder.nativeOrder())
        .asFloatBuffer()
        .put(
            new float[] {
              /*0:*/ -1f, -1f, /*1:*/ +1f, -1f, /*2:*/ -1f, +1f, /*3:*/ +1f, +1f,
            });

final VertexBuffer screenCoordsVertexBuffer =
    new VertexBuffer(render, /* numberOfEntriesPerVertex= */ 3, null);
final VertexBuffer cameraTexCoordsVertexBuffer =
    new VertexBuffer(render, /* numberOfEntriesPerVertex= */ 3, null);

NDC_QUAD_COORDS_BUFFER.rewind();
frame.transformCoordinates3d(
    Coordinates2d.OPENGL_NORMALIZED_DEVICE_COORDINATES,
    NDC_QUAD_COORDS_BUFFER,
    Coordinates3d.EIS_NORMALIZED_DEVICE_COORDINATES,
    screenCoords);
screenCoordsVertexBuffer.set(screenCoords);

NDC_QUAD_COORDS_BUFFER.rewind();
frame.transformCoordinates3d(
    Coordinates2d.OPENGL_NORMALIZED_DEVICE_COORDINATES,
    NDC_QUAD_COORDS_BUFFER,
    Coordinates3d.EIS_TEXTURE_NORMALIZED,
    cameraTexCoords);
cameraTexCoordsVertexBuffer.set(cameraTexCoords);

Kotlin

val COORDS_BUFFER_SIZE_2D = 2 * 4 * Float.SIZE_BYTES
val COORDS_BUFFER_SIZE_3D = 3 * 4 * Float.SIZE_BYTES
val cameraTexCoords =
  ByteBuffer.allocateDirect(COORDS_BUFFER_SIZE_3D)
    .order(ByteOrder.nativeOrder())
    .asFloatBuffer()
val screenCoords =
  ByteBuffer.allocateDirect(COORDS_BUFFER_SIZE_3D)
    .order(ByteOrder.nativeOrder())
    .asFloatBuffer()
val cameraTexCoordsVertexBuffer = VertexBuffer(render, /* numberOfEntriesPerVertex= */ 3, null)
val screenCoordsVertexBuffer = VertexBuffer(render, /* numberOfEntriesPerVertex= */ 3, null)
val NDC_QUAD_COORDS_BUFFER =
  ByteBuffer.allocateDirect(COORDS_BUFFER_SIZE_2D)
    .order(ByteOrder.nativeOrder())
    .asFloatBuffer()
    .apply {
      put(
        floatArrayOf(
          /* 0: */
          -1f,
          -1f,
          /* 1: */
          +1f,
          -1f,
          /* 2: */
          -1f,
          +1f,
          /* 3: */
          +1f,
          +1f
        )
      )
    }
NDC_QUAD_COORDS_BUFFER.rewind()
frame.transformCoordinates3d(
  Coordinates2d.OPENGL_NORMALIZED_DEVICE_COORDINATES,
  NDC_QUAD_COORDS_BUFFER,
  Coordinates3d.EIS_NORMALIZED_DEVICE_COORDINATES,
  screenCoords
)
screenCoordsVertexBuffer.set(screenCoords)

NDC_QUAD_COORDS_BUFFER.rewind()
frame.transformCoordinates3d(
  Coordinates2d.OPENGL_NORMALIZED_DEVICE_COORDINATES,
  NDC_QUAD_COORDS_BUFFER,
  Coordinates3d.EIS_TEXTURE_NORMALIZED,
  cameraTexCoords
)
cameraTexCoordsVertexBuffer.set(cameraTexCoords)

關閉 EIS 時，輸出 3D 座標等同於 2D 座標，只要將 z 值設為不產生任何變更即可。

修改著色器

計算出來的 3D 座標應傳遞至背景算繪著色器。頂點緩衝區現在使用 EIS 為 3D：

layout(location = 0) in vec4 a_Position;
layout(location = 1) in vec3 a_CameraTexCoord;
out vec3 v_CameraTexCoord;
void main() {
  gl_Position = a_Position;
  v_CameraTexCoord = a_CameraTexCoord;
}

此外，片段著色器需要套用透視校正：

precision mediump float;
uniform samplerExternalOES u_CameraColorTexture;
in vec3 v_CameraTexCoord;
layout(location = 0) out vec4 o_FragColor;
void main() {
  vec3 tc = (v_CameraTexCoord / v_CameraTexCoord.z);
  o_FragColor = texture(u_CameraColorTexture, tc.xy);
}

詳情請參閱 hello_eis_kotlin 範例應用程式。