C++超强图片预览器

本文作者原创，首发在本博客；CSDN 上的同名文章已标注为转载并回链到本页：https://blog.csdn.net/qq_30220519/article/details/143254882

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关键代码

uint32_t getSrcPx3(const cv::Mat& srcImg, int srcX, int srcY, int mainX, int mainY) const {
        cv::Vec3b srcPx = srcImg.at<cv::Vec3b>(srcY, srcX);

        intUnion ret = 255;
        if (curPar.zoomCur < curPar.ZOOM_BASE && srcY > 0 && srcX > 0) { // 简单临近像素平均
            cv::Vec3b px0 = srcImg.at<cv::Vec3b>(srcY - 1, srcX - 1);
            cv::Vec3b px1 = srcImg.at<cv::Vec3b>(srcY - 1, srcX);
            cv::Vec3b px2 = srcImg.at<cv::Vec3b>(srcY, srcX - 1);
            for (int i = 0; i < 3; i++)
                ret[i] = (px0[i] + px1[i] + px2[i] + srcPx[i]) / 4;

            return ret.u32;
        }
        ret[0] = srcPx[0];
        ret[1] = srcPx[1];
        ret[2] = srcPx[2];
        return ret.u32;
    }

    uint32_t getSrcPx4(const cv::Mat& srcImg, int srcX, int srcY, int mainX, int mainY) const {
        // 使用 xxx.ptr() 需注意 xxx.step1() 必须等于 xxx.cols*4
        auto srcPtr = (intUnion*)srcImg.ptr();
        int srcW = srcImg.cols;

        intUnion srcPx = srcPtr[srcW * srcY + srcX];
        intUnion bgPx = ((mainX / BG_GRID_WIDTH + mainY / BG_GRID_WIDTH) & 1) ?
            GRID_DARK : GRID_LIGHT;

        if (srcPx[3] == 0) return bgPx.u32;

        intUnion px;
        if (curPar.zoomCur < curPar.ZOOM_BASE && srcY > 0 && srcX > 0) { // 简单临近像素平均
            intUnion srcPx1 = srcPtr[srcW * (srcY - 1) + srcX - 1];
            intUnion srcPx2 = srcPtr[srcW * (srcY - 1) + srcX];
            intUnion srcPx3 = srcPtr[srcW * srcY + srcX - 1];
            for (int i = 0; i < 4; i++)
                px[i] = (srcPx1[i] + srcPx2[i] + srcPx3[i] + srcPx[i]) / 4;
        }
        else {
            px = srcPx;
        }

        if (px[3] == 255) return px.u32;

        const int alpha = px[3];
        intUnion ret = alpha;
        for (int i = 0; i < 3; i++)
            ret[i] = (bgPx[i] * (255 - alpha) + px[i] * alpha) / 256;
        return ret.u32;
    }

    void drawCanvas(const cv::Mat& srcImg, cv::Mat& canvas) const {
        int srcH, srcW;
        if (curPar.rotation == 1 || curPar.rotation == 3) {
            srcH = srcImg.cols;
            srcW = srcImg.rows;
        }
        else {
            srcH = srcImg.rows;
            srcW = srcImg.cols;
        }

        const int canvasH = canvas.rows;
        const int canvasW = canvas.cols;

        if (srcH <= 0 || srcW <= 0)
            return;

        const int deltaW = curPar.slideCur.x + (int)((canvasW - srcW * curPar.zoomCur / curPar.ZOOM_BASE) / 2);
        const int deltaH = curPar.slideCur.y + (int)((canvasH - srcH * curPar.zoomCur / curPar.ZOOM_BASE) / 2);

        int xStart = deltaW < 0 ? 0 : deltaW;
        int yStart = deltaH < 0 ? 0 : deltaH;
        int xEnd = (int)(srcW * curPar.zoomCur / curPar.ZOOM_BASE + deltaW);
        int yEnd = (int)(srcH * curPar.zoomCur / curPar.ZOOM_BASE + deltaH);
        if (xEnd > canvasW) xEnd = canvasW;
        if (yEnd > canvasH) yEnd = canvasH;

        // 使用 xxx.ptr() 需注意 xxx.step1() 必须等于 xxx.cols*4
        memset(canvas.ptr(), BG_COLOR, 4ULL * canvasH * canvasW);

        if (srcImg.type() == CV_8UC3) {
#ifdef ENABLE_OMP
            #pragma omp parallel for
#endif
            for (int y = yStart; y < yEnd; y++) {
                auto ptr = ((uint32_t*)canvas.ptr()) + y * canvasW;
                for (int x = xStart; x < xEnd; x++) {
                    const int srcX = (int)(((int64_t)x - deltaW) * curPar.ZOOM_BASE / curPar.zoomCur);
                    const int srcY = (int)(((int64_t)y - deltaH) * curPar.ZOOM_BASE / curPar.zoomCur);
                    if (0 <= srcX && srcX < srcW && 0 <= srcY && srcY < srcH) {
                        switch (curPar.rotation)
                        {
                        case 1:
                            ptr[x] = getSrcPx3(srcImg, srcH - 1 - srcY, srcX, x, y);
                            break;
                        case 2:
                            ptr[x] = getSrcPx3(srcImg, srcW - 1 - srcX, srcH - 1 - srcY, x, y);
                            break;
                        case 3:
                            ptr[x] = getSrcPx3(srcImg, srcY, srcW - 1 - srcX, x, y);
                            break;
                        default:
                            ptr[x] = getSrcPx3(srcImg, srcX, srcY, x, y);
                            break;
                        }
                    }
                }
            }
        }
        else if (srcImg.type() == CV_8UC4) {
#ifdef ENABLE_OMP
            #pragma omp parallel for
#endif
            for (int y = yStart; y < yEnd; y++) {
                auto ptr = ((uint32_t*)canvas.ptr()) + y * canvasW;
                for (int x = xStart; x < xEnd; x++) {
                    const int srcX = (int)(((int64_t)x - deltaW) * curPar.ZOOM_BASE / curPar.zoomCur);
                    const int srcY = (int)(((int64_t)y - deltaH) * curPar.ZOOM_BASE / curPar.zoomCur);
                    if (0 <= srcX && srcX < srcW && 0 <= srcY && srcY < srcH) {
                        switch (curPar.rotation)
                        {
                        case 1:
                            ptr[x] = getSrcPx4(srcImg, srcH - 1 - srcY, srcX, x, y);
                            break;
                        case 2:
                            ptr[x] = getSrcPx4(srcImg, srcW - 1 - srcX, srcH - 1 - srcY, x, y);
                            break;
                        case 3:
                            ptr[x] = getSrcPx4(srcImg, srcY, srcW - 1 - srcX, x, y);
                            break;
                        default:
                            ptr[x] = getSrcPx4(srcImg, srcX, srcY, x, y);
                            break;
                        }
                    }
                }
            }
        }
    }

效果

参考

GitHub - jark006/jarkViewer: A simple image viewer. 一款简单的看图软件。

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创作不易，小小的支持一下吧！

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