Question of rendering an input cursor

[xland]

I plan to use ThorVG to develop a GUI framework.

This framework will include a text editing control, similar to the <textarea> element in HTML.

Suppose I've rendered a block of text inside this control, and there's an input cursor (caret) blinking between two characters.

That is, every few hundred milliseconds, the cursor (a vertical rectangular bar) needs to be drawn or erased.

Since this input cursor may overlap with the text on either side, does that mean that redrawing the cursor would also require redrawing the text?

If so, wouldn't that affect performance?

Does ThorVG provide any support or optimization for such scenarios?

[hermet]

Hi,

does that mean that redrawing the cursor would also require redrawing the text?

If it's overlapping, then yes — the overlapping paint object will be redrawn by the cursor's dirty regions. However, this doesn't mean you don't need to handle redrawing the text on your side.

If so, wouldn't that affect performance?

with ThorVG v0 (v0.1.x ~ v0.15.x) - Yes
with ThorVG v1 (Since pre-release v1.0-pre23 or main branch) - literally it could affect, but optimally

Does ThorVG provide any support or optimization for such scenarios?

The optimization has been done only for Software Engine now. Please check the doc, its mechanism:
https://github.com/thorvg/thorvg/blob/main/README.md

[xland]

If I remove the true parameter, the final result is not as expected.
I am using the ThorVG 1.0-pre branch.

When I switch ThorVG to the main branch, the caret no longer blinks,
The behavior is different from that in the ThorVG 1.0-pre branch.

[hermet]

Looks like you're adding text multiple times, @_@.

[xland]

You mentioned this earlier, and I paid special attention to it.
There is indeed only one text globally.

In any case, the caret should disappear every 500 milliseconds, right?
But it remains visible all the time.

[hermet]

@xland Yes, please later check of clear() change with v1.0-pre23.

[xland]

@hermet

I tested the latest ThorVG 1.0-pre branch, and the results were different from my expectations.
The current result is: once the cursor appears, it never disappears.

This method is executed every 500 milliseconds.

void MainWindow::paint(tvg::Canvas* canvas)
{
    if (flag) {
        caret->opacity(255);
    }
    else {
        caret->opacity(0);
    }
    flag = !flag;
    canvas->draw(false);
    canvas->sync();
    InvalidateRect(hwnd, nullptr, false);
}

[hermet]

@xland Please check, thanks.

void MainWindow::paint(tvg::Canvas* canvas)
{
    if (flag) {
        caret->opacity(255);
    }
    else {
        caret->opacity(0);
    }
    flag = !flag;
    canvas->update();           // <---------------------- Please call
    canvas->draw(false);
    canvas->sync();
    InvalidateRect(hwnd, nullptr, false);
}

[xland]

After I added canvas->update();, the program's behavior didn't change at all — the input cursor still doesn't blink.
Once I use canvas->draw(true);, the program behaves as expected.
This is the window's redraw code:

    case WM_PAINT: {
        PAINTSTRUCT ps;
        auto hdc = BeginPaint(hwnd, &ps);
        BITMAPINFO bmi = { sizeof(BITMAPINFOHEADER), w, 0 - h, 1, 32, BI_RGB, h * 4 * w, 0, 0, 0, 0 };
        SetDIBitsToDevice(hdc, 0, 0, w, h, 0, 0, 0, h, buffer.data(), &bmi, DIB_RGB_COLORS);
        EndPaint(hwnd, &ps);
        return 0;
    }

The buffer is created like this:

    {
        RECT rect;
        GetClientRect(hwnd, &rect);
        w = rect.right - rect.left;
        h = rect.bottom - rect.top;
    }
    buffer.resize(w * h);  //std::vector<uint32_t> buffer;
    buffer.shrink_to_fit();
    canvas.reset(tvg::SwCanvas::gen());  //std::unique_ptr<tvg::SwCanvas> canvas;
    canvas->target(buffer.data(), w, w, h, tvg::ColorSpace::ARGB8888);

[xland]

The minimal reproducible example is here: https://github.com/xland/ThorVGInput

[hermet]

@xland thanks for report. the fix will be in the thorvg-pre24.

[xland]

After testing ThorVG 1.0.0-pre24, the issue has been resolved