docs: public void drawFrame(int textureId, float[] texMatrix) {
          // Use the identity matrix for MVP so our 2x2 FULL_RECTANGLE covers the viewport.
          mProgram.draw(IDENTITY_MATRIX, mRectDrawable.getVertexArray(), 0,
                  mRectDrawable.getVertexCount(), mRectDrawable.getCoordsPerVertex(),
                  mRectDrawable.getVertexStride(),
                  texMatrix, TEX_COORDS_BUF, textureId, TEX_COORDS_STRIDE);
      }