hwc_overlay

1,

/* this layer is to be drawn into the framebuffer by SurfaceFlinger */

HWC_FRAMEBUFFER;

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

2,

android_vendor_asus_tilapia /proprietary /hwcomposer.tegra3.so

3, 三星驱动

https://bitbucket.org/seandroid/device-samsung-crespo/src/c932ac3b9f8a53a5c433dc7d3cfa2fb5d45a7eb9/libhwcomposer/SecHWC.cpp?at=seandroid

static int hwc_prepare(hwc_composer_device_t *dev, hwc_layer_list_t* list)
{

    struct hwc_context_t* ctx = (struct hwc_context_t*)dev;
    int overlay_win_cnt = 0;
    int compositionType = 0;
    int ret;

    //if geometry is not changed, there is no need to do any work here
    if( !list || (!(list->flags & HWC_GEOMETRY_CHANGED)))
        return 0;

    //all the windows are free here....
    for (int i = 0; i < NUM_OF_WIN; i++) {
        ctx->win[i].status = HWC_WIN_FREE;
        ctx->win[i].buf_index = 0;
    }
    ctx->num_of_hwc_layer = 0;
    ctx->num_of_fb_layer = 0;
    LOGV("%s:: hwc_prepare list->numHwLayers %d", __func__, list->numHwLayers);

    for (int i = 0; i < list->numHwLayers ; i++) {
        hwc_layer_t* cur = &list->hwLayers[i];

        if (overlay_win_cnt < NUM_OF_WIN) {
            compositionType = get_hwc_compos_decision(cur);

            if (compositionType == HWC_FRAMEBUFFER) {
                cur->compositionType = HWC_FRAMEBUFFER;
                ctx->num_of_fb_layer++;
            } else {
                ret = assign_overlay_window(ctx, cur, overlay_win_cnt, i);
                if (ret != 0) {
                    cur->compositionType = HWC_FRAMEBUFFER;
                    ctx->num_of_fb_layer++;
                    continue;
                }

                cur->compositionType = HWC_OVERLAY;
                cur->hints = HWC_HINT_CLEAR_FB;
                overlay_win_cnt++;
                ctx->num_of_hwc_layer++;
            }
        } else {
            cur->compositionType = HWC_FRAMEBUFFER;
            ctx->num_of_fb_layer++;
        }
    }

    if(list->numHwLayers != (ctx->num_of_fb_layer + ctx->num_of_hwc_layer))
        LOGV("%s:: numHwLayers %d num_of_fb_layer %d num_of_hwc_layer %d ",
                __func__, list->numHwLayers, ctx->num_of_fb_layer,
                ctx->num_of_hwc_layer);

    if (overlay_win_cnt < NUM_OF_WIN) {
        //turn off the free windows
        for (int i = overlay_win_cnt; i < NUM_OF_WIN; i++) {
            window_hide(&ctx->win[i]);
            reset_win_rect_info(&ctx->win[i]);
        }
    }
    return 0;
}



static int get_hwc_compos_decision(hwc_layer_t* cur)
{
    if(cur->flags & HWC_SKIP_LAYER || !cur->handle) {
        LOGV("%s::is_skip_layer %d cur->handle %x",
                __func__, cur->flags & HWC_SKIP_LAYER, (uint32_t)cur->handle);
        return HWC_FRAMEBUFFER;
    }

    IMG_native_handle_t *prev_handle = (IMG_native_handle_t *)(cur->handle);
    int compositionType = HWC_FRAMEBUFFER;

    /* check here....if we have any resolution constraints */
    if (((cur->sourceCrop.right - cur->sourceCrop.left) < 16) ||
        ((cur->sourceCrop.bottom - cur->sourceCrop.top) < 8))
        return compositionType;

    if ((cur->transform == HAL_TRANSFORM_ROT_90) ||
        (cur->transform == HAL_TRANSFORM_ROT_270)) {
        if(((cur->displayFrame.right - cur->displayFrame.left) < 4)||
           ((cur->displayFrame.bottom - cur->displayFrame.top) < 8))
            return compositionType;
        } else if (((cur->displayFrame.right - cur->displayFrame.left) < 8) ||
                   ((cur->displayFrame.bottom - cur->displayFrame.top) < 4))
         return compositionType;

    if((prev_handle->usage & GRALLOC_USAGE_PHYS_CONTIG) &&
       (cur->blending == HWC_BLENDING_NONE))
        compositionType = HWC_OVERLAY;
    else
        compositionType = HWC_FRAMEBUFFER;

    LOGV("%s::compositionType %d bpp %d format %x usage %x",
            __func__,compositionType, prev_handle->uiBpp, prev_handle->iFormat,
            prev_handle->usage & GRALLOC_USAGE_PHYS_CONTIG);

    return  compositionType;
}