How to dynamically draw Mosaic effects

[xland]

I want to draw Mosaic effects on an image as the user drags the mouse.
I don't know how to finish this job in the right way.
Hope to get your advice.
Thanks

This's what I want to do.

[kobalicek]

At the moment Blend2D doesn't provide effects, so in order to do this, you would have to manipulate the pixel data yourself.

If you want to apply such a custom effect on area that you want to define by drawing, for example, you can render that to A8 surface and use that as a mask to apply the effect.

[xland]

Thanks very much.
I'll try later and share my code here.

[xland]

Excuse me,
How do I get pixel data at a point in the BLImage or BLImageData?

I try to use these codes to draw mosaic in a box area.

for (size_t y = box.y0; y < box.y1; y += strokeWidth)
{
    for (size_t x = box.x0; x < box.x1; x+=strokeWidth)
    {
        auto index = y * (int)screenW * 4 + x * 4;
        char* data = (char*)(bgImgData->pixelData);
        auto r1 = data[index];
        auto g1 = data[index+1];
        auto b1 = data[index+2];
        auto a1 = data[index+3];
        paintCtx->setFillStyle(BLRgba32(r1, g1, b1, a1));
        paintCtx->fillBox(x, y, x + strokeWidth, y + strokeWidth);
    }
}

This is what i got:

[xland]

char* should be unsigned char*

unsigned char* data = (unsigned char*)(bgImgData->pixelData);

[xland]

Draw a Mosaic blur in a Box area

unsigned char* data = (unsigned char*)(bgImgData->pixelData);
        SetBoxByPos(box,x1, y1,x2, y2);
        for (size_t y = box.y0; y < box.y1; y += strokeWidth)
        {
            for (size_t x = box.x0; x < box.x1; x+=strokeWidth)
            {
                BLPointI points[5];
                //box left top point
                points[0].x = x;
                points[0].y = y;
                //box right top point
                points[1].y = y;
                if (x + strokeWidth > box.x1) {
                    points[1].x = box.x1;
                }
                else
                {
                    points[1].x = x+strokeWidth;
                }
                //center point
                if (x + (int)strokeWidth/2 > box.x1) {
                    points[2].x = x+(int)((box.x1 -x)/2);
                }
                else
                {
                    points[2].x = x + (int)strokeWidth / 2;
                }
                if (y + (int)strokeWidth / 2 > box.y1) {
                    points[2].y = y + (int)((box.y1 - y) / 2);
                }
                else
                {
                    points[2].y = y + (int)strokeWidth / 2;
                }
                //left down point
                points[3].x = x;
                if (y + (int)strokeWidth > box.y1) {
                    points[3].y = box.y1;
                }
                else
                {
                    points[3].y = y + (int)strokeWidth;
                }
                //right down point
                if (x + (int)strokeWidth > box.x1) {
                    points[4].x = box.x1;
                }
                else
                {
                    points[4].x = x + (int)strokeWidth;
                }
                if (y + (int)strokeWidth > box.y1) {
                    points[4].y = box.y1;
                }
                else
                {
                    points[4].y = y + (int)strokeWidth;
                }
                unsigned int b{0}, g{ 0 }, r{ 0 }, a{ 0 };
                for (size_t i = 0; i < 5; i++)
                {
                    auto index = points[i].y * (int)screenW * 4 + points[i].x * 4;
                    b += data[index];
                    g += data[index + 1];
                    r += data[index + 2];
                    a += data[index + 3];
                }
                //5 point colors average
                paintCtx->setFillStyle(BLRgba32(r/5, g/5, b/5, a/5));
                paintCtx->fillBox(x, y, x + strokeWidth, y + strokeWidth);
            }
        }