合成类型

 frameworks/native/services/surfaceflinger./DisplayHardware/HWComposer.cpp

"GLES",
"HWC",
"BACKGROUND",
"FB TARGET",
"UNKNOWN

  

hardware/libhardware/include/hardware/hwcomposer_defs.h

enum {
    /* this layer is to be drawn into the framebuffer by SurfaceFlinger */
    HWC_FRAMEBUFFER = 0,

    /* this layer will be handled in the HWC */
    HWC_OVERLAY = 1,

    /* this is the background layer. it's used to set the background color.
     * there is only a single background layer */
    HWC_BACKGROUND = 2,

    /* this layer holds the result of compositing the HWC_FRAMEBUFFER layers.
     * Added in HWC_DEVICE_API_VERSION_1_1. */
    HWC_FRAMEBUFFER_TARGET = 3,
};