0 Preface

    from 《iTOP4412 VSYNC（4.0.3_r1）》 You know ,android-4.0.3_r1 Not yet supported VSYNC, So what signal triggers its image synthesis ？ This paper makes an in-depth analysis .

Tips：android-4.0.3_r1 Of SurfaceFlinger The source path is frameworks/base/services/surfaceflinger, Subsequent new versions will be migrated to frameworks/native/services/surfaceflinger, For the latter, see 《iTOP4412 SurfaceFlinger（4.4.4_r1）》.

1 The way of synthesis

    It mainly includes HWC_FRAMEBUFFER and HWC_OVERLAY Two synthetic methods ：

/*
 * hwc_layer_t::compositionType values
 */
enum {
    /* this layer is to be drawn into the framebuffer by SurfaceFlinger */
    HWC_FRAMEBUFFER = 0