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_Writing a driver of the DRI engine for your GPU._ |
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_Writing a driver of the DRI engine for your GPU._
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\ No newline at end of file |
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Table of Contents
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- [Overview](#overview)
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* [Compile-time configuration](#compile-time-configuration)
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* [Run-time configuration](#run-time-configuration)
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* [Implement DRI driver](#implement-dri-driver)
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* [Restrictions](#restrictions)
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- [Example](#example)
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## Overview
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In order to support modern graphics card or GPU, we introduced a
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new NEWGAL engine of `dri`. The developer can use this engine to
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run MiniGUI apps on a Linux box on which the DRI
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(Direct Rendering Infrastructure) is enabled.
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The `dri` engine uses `libdrm` developed by Free Desktop project:
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https://dri.freedesktop.org/wiki/
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Libdrm is a user-space library implements the Direct Rendering Manager.
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MiniGUI mainly uses this library to support the dumb frame buffer
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(no hardware acceleration). However, you can write a driver for your
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graphics card or GPU to implement the hardware accelerated features.
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To avoid modifying the MiniGUI source code when supporting a new GPU,
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the `dri` engine has adopted a scalable design:
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* You can directly use the `dri` engine to run MiniGUI on a GPU
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which supports dumb frame buffer.
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* When you want to take advantage of the hardware acceleration of
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your GPU, you can write some code for your GPU as a sub driver
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of `dri` engine outside MiniGUI.
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This document describes how to enable `dri` engine and write a
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hardware-accelerated driver for your own GPU.
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Note that, generally, the driver will be implemented by the GPU
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or SoC vendors. The MiniGUI app developers do not need to
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care about this.
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### Compile-time configuration
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There are two configure options related to the `dri` engine:
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* `--enable-videodri` enables the `dri` engine, and `--disable-videodri`
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disables the `dri` engine. Note that the `dri` engine is only
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available on Linux, and you need to install the `libdrm` 2.4 or later
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first.
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* `--with-targetname=external`. When you configure MiniGUI with this
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option. MiniGUI will use the external function `__dri_ex_driver_get`
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to initialize the DRI driver. If you do not implement this function,
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the link will fail.
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### Run-time configuration
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For `dri` engine, we introduce a new section in MiniGUI runtime
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configuration:
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```
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[dri]
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defaultmode=1024x768-32bpp
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dpi=96
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pixelformat=XR24
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device=/dev/dri/card0
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```
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You can use the key `dri.device` to specify your DRI device.
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You can use the key `dri.pixelformat` to specify the DRM pixel format for the
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screen. We use DRM fourcc code to defined the pixel format of the screen
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surface. For more information, please see `<drm/drm_fourcc.h>` header file.
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Note that only 8/16/24/32 bpp RGB formats are supported. For example, `XR24`
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means `X8R8G8B8` pixel format.
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### Implement DRI driver
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The header file `<minigui/exstubs.h>` defines the operators (a set of
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callback functions) you need to implement for your GPU externally.
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To exploit the GPU's accelerated rendering capabilities, a MiniGUI app
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can use `cairo` and/or `OpenGL ES` to assist in rendering 2D/3D graphics
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when using the `dri` engine. We will provide some samples in `mg-tests`
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or `mg-samples` for this purpose.
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### Restrictions
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In version 4.0.0, the `dri` NEWGAL engine does not provide support for
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MiniGUI-Processes run-time mode. We will enhance this in the subsequent
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version of MiniGUI.
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Also note that when you use the hardware accelerated sub driver, MiniGUI app
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may need the root privilege to call `drmSetMaster` to set the video mode.
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However, under MiniGUI-Processes run-time mode, only the server (`mginit`) will
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need this privilege when you use the future `dri` engine.
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## Example
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As an example, we implement the sub driver for `i915` graphics chard
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in `mg-tests/dri-engine/`. Please refer to `mg-tests` repository:
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https://github.com/VincentWei/mg-tests/tree/master/dri-engine
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