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Bug 1594500 - Document the memory layout of brush vertex shaders. r=gw

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Differential Revision: https://phabricator.services.mozilla.com/D52138

--HG--
extra : moz-landing-system : lando
This commit is contained in:
Nicolas Silva 2019-11-08 09:51:10 +00:00
parent 7296de4e10
commit a443a5a79d
1 changed files with 45 additions and 0 deletions
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45
gfx/wr/webrender/res/brush.glsl
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@ -2,6 +2,51 @@
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/// # Brush vertex shaders memory layout
///
/// The overall memory layout is the same for all brush shaders.
///
/// The vertex shader receives a minimal amount of data from vertex attributes (packed into a single
/// ivec4 per instance) and the rest is fetched from various uniform samplers using offsets decoded
/// from the vertex attributes.
///
/// The diagram below shows the the various pieces of data fectched in the vertex shader:
///
///```ascii
/// (sPrimitiveHeadersI)
/// (VBO) +-----------------------+
/// +----------------------------+ +----------------------------> | Int header |
/// | Instance vertex attributes | | (sPrimitiveHeadersF) | |
/// | | | +---------------------+ | z |
/// | x: prim_header_address +-------+---> | Float header | | specific_address +-----+
/// | y: picture_task_address +---------+ | | | transform_address +---+ |
/// | clip_address +-----+ | | local_rect | | user_data | | |
/// | z: flags | | | | local_clip_rect | +-----------------------+ | |
/// | segment_index | | | +---------------------+ | |
/// | w: resource_address +--+ | | | |
/// +----------------------------+ | | | (sGpuCache) | |
/// | | | (sGpuCache) +------------+ | |
/// | | | +---------------+ | Transform | <--------+ |
/// (sGpuCache) | | +-> | Picture task | +------------+ |
/// +-------------+ | | | | |
/// | Resource | <---+ | | ... | |
/// | | | +---------------+ +--------------------------------+
/// | | | |
/// +-------------+ | (sGpuCache) v (sGpuCache)
/// | +---------------+ +--------------+---------------+-+-+
/// +-----> | Clip area | | Brush data | Segment data | | |
/// | | | | | | |
/// | ... | | ... | ... | | | ...
/// +---------------+ +--------------+---------------+-+-+
///```
///
/// - Segment data address is obtained by combining the address stored in the int header and the
/// segment index decoded from the vertex attributes.
/// - Resource data is optional, some brush types (such as images) store some extra data there while
/// other brush types don't use it.
///
#ifdef WR_VERTEX_SHADER
void brush_vs(