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updated the tutorial

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kallaballa 2 years ago
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  1. 216
      modules/viz2d/tutorials/00-intro.markdown

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modules/viz2d/tutorials/00-intro.markdown
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@ -1,5 +1,7 @@
# Viz2D {#viz2d}
[TOC]
# What is Viz2D?
Viz2D is a way of writing graphical (on- and offscreen) high performance applications with OpenCV. It is light-weight and unencumbered by QT or GTK licenses. It features vector graphics using [NanoVG](https://github.com/inniyah/nanovg) a GUI based on [NanoGUI](https://github.com/mitsuba-renderer/nanogui) and (on supported systems) OpenCL/OpenGL and OpenCL/VAAPI interoperability. It should be included in [OpenCV-contrib](https://github.com/opencv/opencv_contrib) once it is ready.
@ -62,226 +64,44 @@ Those are minimal examples, full samples below.
## Display an image
Actually there are several ways to display an image but for now we focus on the most convinient way.
@code{.cpp}
Ptr<Viz2D> v2d = Viz2D::make(Size(WIDTH, HEIGHT), "Show image");
//An image
UMat image = imread("sample.png");
//Feeds the image to the video pipeline
v2d->feed(image);
//Display the framebuffer in the native window
v2d->display();
@endcode
@include samples/cpp/display_image.cpp
This will create a window with size WIDTHxHEIGHT for on-screen rendering with the title "Show Image" and display the image (using the video pipeline which resizes the image to framebuffer size, but more about that later).
### Render OpenGL
## Render OpenGL
This example renders a rotating tetrahedron using legacy OpenGL for brevity.
@code{.cpp}
Ptr<Viz2D> v2d = Viz2D::make(Size(WIDTH, HEIGHT), "GL Tetrahedron");
v2d->gl([](const Size sz) {
//Initialize the OpenGL scene
glViewport(0, 0, sz.width, sz.height);
glColor3f(1.0, 1.0, 1.0);
glEnable(GL_CULL_FACE);
glCullFace(GL_BACK);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glFrustum(-2, 2, -1.5, 1.5, 1, 40);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0, 0, -3);
glRotatef(50, 1, 0, 0);
glRotatef(70, 0, 1, 0);
});
//Viz2D::run() though it takes a functor is not a context. It is simply an abstraction
//of a run loop for portability reasons and executes the functor until the application
//terminates or the functor returns false.
v2d->run([]() {
v2d->gl([](const Size& sz) {
//Render a tetrahedron using immediate mode because the code is more concise
glViewport(0, 0, sz.width, sz.height);
glRotatef(1, 0, 1, 0);
glClearColor(0.0f, 0.0f, 1.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_TRIANGLE_STRIP);
glColor3f(1, 1, 1);
glVertex3f(0, 2, 0);
glColor3f(1, 0, 0);
glVertex3f(-1, 0, 1);
glColor3f(0, 1, 0);
glVertex3f(1, 0, 1);
glColor3f(0, 0, 1);
glVertex3f(0, 0, -1.4);
glColor3f(1, 1, 1);
glVertex3f(0, 2, 0);
glColor3f(1, 0, 0);
glVertex3f(-1, 0, 1);
glEnd();
});
//If onscreen rendering is enabled it displays the framebuffer in the native window.
//Returns false if the window was closed.
return v2d->display();
});
@endcode
@include samples/cpp/render_opengl.cpp
### Manipulate the framebuffer using OpenCV/OpenCL
## Manipulate the framebuffer using OpenCV/OpenCL
All contexts operate on the same framebuffer through different means. OpenCV (using OpenCL where available) can manipulate results of other contexts throught the ```fb``` context.
@code{.cpp}
Ptr<Viz2D> v2d = Viz2D::make(Size(WIDTH, HEIGHT), "Manipulate Framebuffer");
//An image
UMat image = imread("sample.png");
//Feeds the image to the video pipeline
v2d->feed(image);
//Directly access the framebuffer using OpenCV
v2d->fb([](UMat& framebuffer) {
flip(framebuffer,framebuffer,0); //Flip the framebuffer
});
//Display the upside-down image in the native window
v2d->display();
@endcode
@include samples/cpp/manipulate_fb.cpp
### Vector graphics
## Vector graphics
Through the nvg context javascript-like canvas-rendering is possible.
@code{.cpp}
Ptr<Viz2D> v2d = Viz2D::make(Size(WIDTH, HEIGHT), "Vector Graphics");
//Creates a NanoVG context and draws a cross-hair on the framebuffer
v2d->nvg([](const Size sz) {
//calls from this namespace may only be used inside a nvg context
namespace cv::viz::nvg;
beginPath();
strokeWidth(3.0);
strokeColor(Scalar(0,0,255,255)); //BGRA
moveTo(0, WIDTH/2.0);
lineTo(HEIGHT, WIDTH/2.0);
moveTo(HEIGHT/2.0, 0);
lineTo(HEIGHT/2.0, WIDTH);
stroke();
});
v2d->display()
@endcode
@include samples/cpp/vector_graphics.cpp
### Vector graphics and framebuffer manipulation
## Vector graphics and framebuffer manipulation
The framebuffer can be accessed directly to manipulate data created in other contexts.
@code{.cpp}
Ptr<Viz2D> v2d = Viz2D::make(Size(WIDTH, HEIGHT), "Vector Graphics");
//Creates a NanoVG context and draws a cross-hair on the framebuffer
v2d->nvg([](const Size sz) {
namespace cv::viz::nvg;
beginPath();
strokeWidth(3.0);
strokeColor(Scalar(0,0,255,255)); //BGRA
moveTo(0, WIDTH/2.0);
lineTo(HEIGHT, WIDTH/2.0);
moveTo(HEIGHT/2.0, 0);
lineTo(HEIGHT/2.0, WIDTH);
stroke();
});
v2d->fb([](UMat& framebuffer) {
//Blurs the crosshair using a cheap boxFilter
boxFilter(framebuffer, framebuffer, -1, Size(5, 5), Point(-1,-1), true, BORDER_REPLICATE);
});
v2d->display()
@endcode
@include samples/cpp/vector_graphics_and_fb.cpp
### Font rendering
## Font rendering
Draws "hello world" to the screen.
@code{.cpp}
string hw = "hello world";
Ptr<Viz2D> v2d = Viz2D::make(Size(WIDTH, HEIGHT), "Vector Graphics");
//Clear with black
v2d->clear();
//Render the text at the center of the screen
v2d->nvg([&](const Size& sz) {
using namespace cv::viz::nvg;
fontSize(font_size);
fontFace("sans-bold");
fillColor(Scalar(255, 0, 0, 255));
textAlign(NVG_ALIGN_CENTER | NVG_ALIGN_TOP);
text(WIDTH / 2.0, HEIGHT / 2.0, hw.c_str(), hw.c_str() + hw.size());
});
v2d->display()
@endcode
@include samples/cpp/font_rendering.cpp
### Video editing
## Video editing
Through adding a Source and a Sink v2d becomes capable of video editing. Reads a video, renders text on top and writes the result.
@code{.cpp}
string hw = "hello video!";
Ptr<Viz2D> v2d = Viz2D::make(Size(WIDTH, HEIGHT), "Video Editing");
//Make the video source
Source src = makeCaptureSource("input.webm");
//Make the video sink
Sink sink = makeWriterSink("output.webm", VideoWriter::fourcc('V', 'P', '9', '0'), src.fps(), Size(WIDTH, HEIGHT));
//Attach source and sink
v2d->setSource(src);
v2d->setSink(sink);
v2d->run([]() {
if(!v2d->capture())
return false;
v2d->nvg([&](const Size& sz) {
using namespace cv::viz::nvg;
fontSize(font_size);
fontFace("sans-bold");
fillColor(Scalar(255, 0, 0, 255));
textAlign(NVG_ALIGN_CENTER | NVG_ALIGN_TOP);
text(WIDTH / 2.0, y, hw.c_str(), hw.c_str() + hw.size());
});
v2d->write();
return v2d->display();
});
@endcode
@include samples/cpp/video_editing.cpp
### Font rendering with form based GUI
Draws "hello world" to the screen and let's you control the font size and color with a GUI based on FormHelper.
## Font rendering with form based GUI
Draws "Hello World" to the screen and let's you control the font size and color with a GUI based on FormHelper.
@code{.cpp}
Ptr<Viz2D> v2d = Viz2D::make(Size(WIDTH, HEIGHT), "Vector Graphics");
//The text color. NanoGUI uses rgba with floating point
nanogui::Color textColor = {0.0, 0.0, 1.0, 1.0};
//The font size
float fontSize = 40.0f;
//The text
string hw = "hello world";
//Setup the GUI
v2d->nanogui([&](FormHelper& form) {
//Create a light-weight dialog
form.makeDialog(5, 30, "Settings");
//Create a group
form.makeGroup("Font");
//Create a from variable. The type of widget is deduced from the variable type.
form.makeFormVariable("Font Size", fontSize, 1.0f, 100.0f, true, "pt", "Font size of the text crawl");
//Create a color picker
form.makeColorPicker("Text Color", textColor, "The text color");
});
v2d->run([]() {
v2d->clear();
//Render the text at the center of the screen
v2d->nvg([&](const Size& sz) {
using namespace cv::viz::nvg;
fontSize(fontSize);
fontFace("sans-bold");
fillColor(Scalar(textColor.b() * 255, textColor.g() * 255, textColor.r() * 255, 255));
textAlign(NVG_ALIGN_CENTER | NVG_ALIGN_TOP);
text(WIDTH / 2.0, HEIGHT / 2.0, hw.c_str(), hw.c_str() + hw.size());
});
return v2d->display()
});
@endcode
@include samples/cpp/font_with_gui.cpp
# Samples
The goal of the samples is to show how to use Viz2D to the fullest. Also they show how to use Viz2D in conjunction with interop options to create programs that run mostly (the part the matters) on the GPU. You ***only*** need to build my fork of OpenCV 4.x if you want to use cl-gl sharing on recent Intel platforms (Gen8 - Gen12).

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