diff --git a/doc/dma-buf.dox b/doc/dma-buf.dox index d94a06a85..8214f6f0a 100644 --- a/doc/dma-buf.dox +++ b/doc/dma-buf.dox @@ -1,7 +1,7 @@ /** \page page_dma_buf DMA-BUF Sharing PipeWire supports sharing Direct Memory Access buffers (DMA-BUFs) between -clients via the `SPA_DATA_DmaBuf` data type. However properly negotiating +clients via the \ref SPA_DATA_DmaBuf data type. However properly negotiating DMA-BUF support on both the producer and the consumer side require following a specific procedure. This page describes said procedure by using events and methods from the filter or stream API. @@ -21,37 +21,37 @@ allocating the buffers. ## pw_stream_connect -The stream parameters should contain two `SPA_PARAM_EnumFormat` objects for +The stream parameters should contain two \ref SPA_PARAM_EnumFormat objects for each format: one for DMA-BUFs, one for shared memory buffers as a fallback. Query the list of all supported modifiers from your graphics API of choice. -Add a `SPA_FORMAT_VIDEO_modifier` property to the first stream parameter with +Add a \ref SPA_FORMAT_VIDEO_modifier property to the first stream parameter with the flags `SPA_POD_PROP_FLAG_MANDATORY | SPA_POD_PROP_FLAG_DONT_FIXATE`. The -value of the property should be set to a `SPA_CHOICE_Enum` containing one +value of the property should be set to a \ref SPA_CHOICE_Enum containing one `long` choice per supported modifier, plus `DRM_FORMAT_MOD_INVALID` if the graphics API supports modifier-less buffers. Note: When a producer is only supporting modifier-less buffers it can omit -the `SPA_POD_PROP_FLAG_DONT_FIXATE` (see param_changed hook, For producers). +the \ref SPA_POD_PROP_FLAG_DONT_FIXATE (see param_changed hook, For producers). -The second stream parameter should not contain any `SPA_FORMAT_VIDEO_modifier` +The second stream parameter should not contain any \ref SPA_FORMAT_VIDEO_modifier property. -To prioritise DMA-BUFs place those `SPA_PARAM_EnumFormat` containing modifiers +To prioritise DMA-BUFs place those \ref SPA_PARAM_EnumFormat containing modifiers first, when emitting them to PipeWire. ## param_changed Hook -When the `param_changed` hook is called for a `SPA_PARAM_Format` the client +When the `param_changed` hook is called for a \ref SPA_PARAM_Format the client has to parse the `spa_pod` directly. Use `spa_pod_find_prop(param, NULL, SPA_FORMAT_VIDEO_modifier)` to check whether modifiers were negotiated. If they were negotiated, set the -`SPA_PARAM_BUFFERS_dataType` property to `1 << SPA_DATA_DmaBuf`. If they were +\ref SPA_PARAM_BUFFERS_dataType property to `1 << SPA_DATA_DmaBuf`. If they were not negotiated, fall back to shared memory by setting the -`SPA_PARAM_BUFFERS_dataType` property to `1 << SPA_DATA_MemFd`, +\ref SPA_PARAM_BUFFERS_dataType property to `1 << SPA_DATA_MemFd`, `1 << SPA_DATA_MemPtr`, or both. -While consumers only have to parse the resulting `SPA_PARAM_Format` for any +While consumers only have to parse the resulting \ref SPA_PARAM_Format for any format related information, it's up to the producer to fixate onto a single format modifier pair. The producer is also responsible to check if all clients announce sufficient capabilities or fallback to shared memory buffers when @@ -59,7 +59,7 @@ possible. ### For Consumers -Use `spa_format_video_raw_parse` to get the format and modifier. +Use \ref spa_format_video_raw_parse to get the format and modifier. ### For Producers @@ -70,28 +70,28 @@ modifier-aware one, or supporting both. - modifier-less: In this case only the modifier `DRM_FORMAT_MOD_INVALID` was announced with the format. - It is sufficient to check if the `SPA_PARAM_Format` contains the modifier + It is sufficient to check if the \ref SPA_PARAM_Format contains the modifier property as described above. If that is the case, use DMA-BUFs for screen-sharing, else fall back to SHM, if possible. - modifier-aware: In this case a list with all supported modifiers will be returned in the format. (using `DRM_FORMAT_MOD_INVALID` as the token for the modifier-less API). On the `param_changed` event check if the modifier key is present and has the flag - `SPA_POD_PROP_FLAG_DONT_FIXATE` attached to it. In this case, extract all modifiers + \ref SPA_POD_PROP_FLAG_DONT_FIXATE attached to it. In this case, extract all modifiers from the list and do a test allocation with your allocator to choose the preferred - modifier. Fixate on that `EnumFormat` by announcing a `SPA_PARAM_EnumFormat` with - only one modifier in the `SPA_CHOICE_Enum` and without the - `SPA_POD_PROP_FLAG_DONT_FIXATE` flag, followed by the previous announced - `EnumFormat`. This will retrigger the `param_changed` event with an - `SPA_PARAM_Format` as described below. - If the `SPA_PARAM_Format` contains a modifier key, without the flag - `SPA_POD_PROP_FLAG_DONT_FIXATE`, it should only contain one value in the - `SPA_CHOICE_Enum`. In this case announce the `SPA_PARAM_Buffers` accordingly + modifier. Fixate on that \ref EnumFormat by announcing a \ref SPA_PARAM_EnumFormat with + only one modifier in the \ref SPA_CHOICE_Enum and without the + \ref SPA_POD_PROP_FLAG_DONT_FIXATE flag, followed by the previous announced + \ref EnumFormat. This will retrigger the `param_changed` event with an + \ref SPA_PARAM_Format as described below. + If the \ref SPA_PARAM_Format contains a modifier key, without the flag + \ref SPA_POD_PROP_FLAG_DONT_FIXATE, it should only contain one value in the + \ref SPA_CHOICE_Enum. In this case announce the \ref SPA_PARAM_Buffers accordingly to the selected format and modifier. It is important to query the plane count of the used format modifier pair and set `SPA_PARAM_BUFFERS_blocks` accordingly. Note: When test allocating a buffer, collect all possible modifiers, while omitting -`DRM_FORMAT_MOD_INVALID` from the `SPA_FORMAT_VIDEO_modifier` property and +`DRM_FORMAT_MOD_INVALID` from the \ref SPA_FORMAT_VIDEO_modifier property and pass them all to the graphics API. If the allocation fails and the list of possible modifiers contains `DRM_FORMAT_MOD_INVALID`, fall back to allocating without an explicit modifier if the graphics API allows it. @@ -106,9 +106,9 @@ Allocate a DMA-BUF only using the negotiated format and modifier. This is relevant for consumers. -Check the type of the dequeued buffer. If its `SPA_DATA_MemFd` or -`SPA_DATA_MemPtr` use the fallback SHM import mechanism. -If it's `SPA_DATA_DmaBuf` +Check the type of the dequeued buffer. If its \ref SPA_DATA_MemFd or +\ref SPA_DATA_MemPtr use the fallback SHM import mechanism. +If it's \ref SPA_DATA_DmaBuf get the DMA-BUF FDs (the plane count is encoded in the `n_datas` variable of the `spa_buffer` struct) and import them with the graphics API. @@ -150,15 +150,18 @@ via the filedescriptor. # SPA param video format helpers SPA offers helper functions to parse and build a spa_pod object to/from the spa_video_info_* -struct. The flags `SPA_VIDEO_FLAG_MODIFIER` and `SPA_VIDEO_FLAG_MODIFIER_FIXATION_REQUIRED` +struct. The flags \ref SPA_VIDEO_FLAG_MODIFIER and \ref SPA_VIDEO_FLAG_MODIFIER_FIXATION_REQUIRED are used to indicate modifier usage with the format. `SPA_VIDEO_FLAG_MODIFIER` declares the parsed/provided spa_video_info_* struct contains valid modifier information. For legacy reasons `spa_format_video_*_build` will announce any modifier != 0 even when this flag is unused. `SPA_VIDEO_FLAG_MODIFIER_FIXATION_REQUIRED` is exclusive to the parse helpers and declares that the parsed spa_pod contains modifier information which needs to be fixated as -described aboath. The list of available modifiers has to be parsed manually from the spa_pod +described above. The list of available modifiers has to be parsed manually from the spa_pod object. +- \ref spa_video_info_raw, \ref spa_format_video_raw_parse, \ref spa_format_video_raw_build +- \ref spa_video_info_dsp, \ref spa_format_video_dsp_parse, \ref spa_format_video_dsp_build + # v4l2 Another use case for streaming via DMA-BUFs are exporting a camera feed from v4l2