130 lines
4.2 KiB
Markdown
130 lines
4.2 KiB
Markdown
---
|
|
layout: default
|
|
title: Hello World! on Desktop (C++)
|
|
parent: Getting Started
|
|
nav_order: 5
|
|
---
|
|
|
|
# Hello World! on Desktop (C++)
|
|
{: .no_toc }
|
|
|
|
1. TOC
|
|
{:toc}
|
|
---
|
|
|
|
1. Ensure you have a working version of MediaPipe. See
|
|
[installation instructions](./install.md).
|
|
|
|
2. To run the [`hello world`] example:
|
|
|
|
```bash
|
|
$ git clone https://github.com/google/mediapipe.git
|
|
$ cd mediapipe
|
|
|
|
$ export GLOG_logtostderr=1
|
|
# Need bazel flag 'MEDIAPIPE_DISABLE_GPU=1' as desktop GPU is not supported currently.
|
|
$ bazel run --define MEDIAPIPE_DISABLE_GPU=1 \
|
|
mediapipe/examples/desktop/hello_world:hello_world
|
|
|
|
# It should print 10 rows of Hello World!
|
|
# Hello World!
|
|
# Hello World!
|
|
# Hello World!
|
|
# Hello World!
|
|
# Hello World!
|
|
# Hello World!
|
|
# Hello World!
|
|
# Hello World!
|
|
# Hello World!
|
|
# Hello World!
|
|
```
|
|
|
|
3. The [`hello world`] example uses a simple MediaPipe graph in the
|
|
`PrintHelloWorld()` function, defined in a [`CalculatorGraphConfig`] proto.
|
|
|
|
```C++
|
|
::mediapipe::Status PrintHelloWorld() {
|
|
// Configures a simple graph, which concatenates 2 PassThroughCalculators.
|
|
CalculatorGraphConfig config = ParseTextProtoOrDie<CalculatorGraphConfig>(R"(
|
|
input_stream: "in"
|
|
output_stream: "out"
|
|
node {
|
|
calculator: "PassThroughCalculator"
|
|
input_stream: "in"
|
|
output_stream: "out1"
|
|
}
|
|
node {
|
|
calculator: "PassThroughCalculator"
|
|
input_stream: "out1"
|
|
output_stream: "out"
|
|
}
|
|
)");
|
|
```
|
|
|
|
You can visualize this graph using
|
|
[MediaPipe Visualizer](https://viz.mediapipe.dev) by pasting the
|
|
CalculatorGraphConfig content below into the visualizer. See
|
|
[here](../tools/visualizer.md) for help on the visualizer.
|
|
|
|
```bash
|
|
input_stream: "in"
|
|
output_stream: "out"
|
|
node {
|
|
calculator: "PassThroughCalculator"
|
|
input_stream: "in"
|
|
output_stream: "out1"
|
|
}
|
|
node {
|
|
calculator: "PassThroughCalculator"
|
|
input_stream: "out1"
|
|
output_stream: "out"
|
|
}
|
|
```
|
|
|
|
This graph consists of 1 graph input stream (`in`) and 1 graph output stream
|
|
(`out`), and 2 [`PassThroughCalculator`]s connected serially.
|
|
|
|
|
|
|
|
4. Before running the graph, an `OutputStreamPoller` object is connected to the
|
|
output stream in order to later retrieve the graph output, and a graph run
|
|
is started with [`StartRun`].
|
|
|
|
```c++
|
|
CalculatorGraph graph;
|
|
MP_RETURN_IF_ERROR(graph.Initialize(config));
|
|
MP_ASSIGN_OR_RETURN(OutputStreamPoller poller,
|
|
graph.AddOutputStreamPoller("out"));
|
|
MP_RETURN_IF_ERROR(graph.StartRun({}));
|
|
```
|
|
|
|
5. The example then creates 10 packets (each packet contains a string "Hello
|
|
World!" with Timestamp values ranging from 0, 1, ... 9) using the
|
|
[`MakePacket`] function, adds each packet into the graph through the `in`
|
|
input stream, and finally closes the input stream to finish the graph run.
|
|
|
|
```c++
|
|
for (int i = 0; i < 10; ++i) {
|
|
MP_RETURN_IF_ERROR(graph.AddPacketToInputStream("in",
|
|
MakePacket<std::string>("Hello World!").At(Timestamp(i))));
|
|
}
|
|
MP_RETURN_IF_ERROR(graph.CloseInputStream("in"));
|
|
```
|
|
|
|
6. Through the `OutputStreamPoller` object the example then retrieves all 10
|
|
packets from the output stream, gets the string content out of each packet
|
|
and prints it to the output log.
|
|
|
|
```c++
|
|
mediapipe::Packet packet;
|
|
while (poller.Next(&packet)) {
|
|
LOG(INFO) << packet.Get<string>();
|
|
}
|
|
```
|
|
|
|
[`hello world`]: https://github.com/google/mediapipe/tree/master/mediapipe/examples/desktop/hello_world/hello_world.cc
|
|
[`CalculatorGraphConfig`]: https://github.com/google/mediapipe/tree/master/mediapipe/framework/calculator.proto
|
|
[`PassThroughCalculator`]: https://github.com/google/mediapipe/tree/master/mediapipe/calculators/core/pass_through_calculator.cc
|
|
[`MakePacket`]: https://github.com/google/mediapipe/tree/master/mediapipe/framework/packet.h
|
|
[`StartRun`]: https://github.com/google/mediapipe/tree/master/mediapipe/framework/calculator_graph.h
|