From 7ccf148f5066ceb1a161f0d7a7d66f75c6e8d420 Mon Sep 17 00:00:00 2001 From: Jesse Hall Date: Wed, 13 Nov 2013 14:48:15 -0800 Subject: Update HWC documentation for virtual displays Bug: 8316155 Change-Id: I56598551b07082bfff90df160b103a4158e8c8c9 --- include/hardware/hwcomposer.h | 32 +++++++++++++++++++++++--------- 1 file changed, 23 insertions(+), 9 deletions(-) diff --git a/include/hardware/hwcomposer.h b/include/hardware/hwcomposer.h index 846bab49..86479d3c 100644 --- a/include/hardware/hwcomposer.h +++ b/include/hardware/hwcomposer.h @@ -315,8 +315,8 @@ typedef struct hwc_display_contents_1 { hwc_surface_t sur; }; - /* WARNING: These fields are for experimental virtual display support, - * and are not currently used. */ + /* These fields are used for virtual displays when the h/w composer + * version is at least HWC_DEVICE_VERSION_1_3. */ struct { /* outbuf is the buffer that receives the composed image for * virtual displays. Writes to the outbuf must wait until @@ -324,14 +324,28 @@ typedef struct hwc_display_contents_1 { * writes to outbuf are complete should be returned in * retireFenceFd. * - * This field will not be updated until after prepare(). If - * prepare() sets all non-FB layers to OVERLAY or sets all non-FB - * layers to FRAMEBUFFER, then the FRAMEBUFFER_TARGET buffer and - * the output buffer may be the same. In mixed OVERLAY/FRAMEBUFFER - * configurations they will have different buffers so the - * h/w composer does not have to read and write the same buffer. + * This field is set before prepare(), so properties of the buffer + * can be used to decide which layers can be handled by h/w + * composer. * - * For physical displays, outbuf will be NULL. + * If prepare() sets all layers to FRAMEBUFFER, then GLES + * composition will happen directly to the output buffer. In this + * case, both outbuf and the FRAMEBUFFER_TARGET layer's buffer will + * be the same, and set() has no work to do besides managing fences. + * + * If the TARGET_FORCE_HWC_FOR_VIRTUAL_DISPLAYS board config + * variable is defined (not the default), then this behavior is + * changed: if all layers are marked for FRAMEBUFFER, GLES + * composition will take place to a scratch framebuffer, and + * h/w composer must copy it to the output buffer. This allows the + * h/w composer to do format conversion if there are cases where + * that is more desirable than doing it in the GLES driver or at the + * virtual display consumer. + * + * If some or all layers are marked OVERLAY, then the framebuffer + * and output buffer will be different. As with physical displays, + * the framebuffer handle will not change between frames if all + * layers are marked for OVERLAY. */ buffer_handle_t outbuf; -- cgit v1.2.3