文章目录
概要
在视频监控系统中，经常需要查看视频画面中的细节。通过实现区域放大、滚轮缩放和拖拽平移等功能，可以让用户更方便地观察视频细节。本文介绍如何在 Windows 系统下实现这些交互功能。
一、功能说明
框选缩放功能：按住鼠标左键，移动鼠标画出矩形框，松开左键，会将框选区域放大至整个窗口显示。点击鼠标右键，即恢复显示原画面。
鼠标滚轮缩放功能：通过鼠标滚轮控制缩放比例，以鼠标所在位置为中心进行缩放。
鼠标拖拽功能：在放大状态下，按住左键可以拖动视频画面，查看不同区域。
二、核心实现代码
cpp
// 检查区域
bool IsValidZoomRc(const RECT *pRC) {
return pRC != nullptr && abs(pRC->left - pRC->right) > 4 && abs(pRC->top - pRC->bottom) > 4;
}
// 左上右下位置相反时对调
inline void fmtRect(RECT &rc) {
if (rc.left > rc.right) std::swap(rc.left, rc.right);
if (rc.top > rc.bottom) std::swap(rc.top, rc.bottom);
}
// 播放类
class CPlayer {
// ...省略其他代码
private:
bool m_bZoom; // 是否启用缩放功能
HANDLE m_hPlayer; // 调用播放库的句柄
POINT m_ptDragStart; // 拖动起始点
RECT m_rcDragStart; // 拖动开始时的显示区域
AV_STREAM_INFO m_stStreamInfo; // 存放流信息的结构体
RECT m_rcZoom; // 记录当前显示的画面区域
RECT m_rcDrawRect; // 用于画框
// 在播放库回调出来的句柄上画框选的方框
void OnVideoDraw(HANDLE handle, HDC hdc) {
if (m_bZoom) {
auto oldPen = SelectObject(hdc, m_hDrawPen);
auto oldBrush = SelectObject(hdc, m_hDrawBrush);
Rectangle(hdc, m_rcDrawRect.left, m_rcDrawRect.top, m_rcDrawRect.right, m_rcDrawRect.bottom);
SelectObject(hdc, oldPen);
SelectObject(hdc, oldBrush);
}
}
// 画框缩放接口
void DoZoom(int wndWidth, int wndHeight, const RECT *pRc, bool bLRButtonUp) {
if (!m_bZoom && m_hPlayer != (void*)INFINITE) {
HS_ShowRect(m_hPlayer, nullptr); // 调用播放库接口，还原画面
return;
}
if (pRc != nullptr) {
// 如果画面已经处于放大状态，不再支持画框
if (((m_rcZoom.right - m_rcZoom.left) != m_stStreamInfo.nWidth) ||
((m_rcZoom.bottom - m_rcZoom.top) != m_stStreamInfo.nHeight)) {
return;
}
}
if (bLRButtonUp || pRc == nullptr) {
ZeroMemory(&m_rcDrawRect, sizeof(m_rcDrawRect));
} else {
m_rcDrawRect = *pRc;
}
double fWndWidth = wndWidth;
double fWndHeight = wndHeight;
if (bLRButtonUp) {
if (pRc == nullptr) {
if (m_hPlayer != (void*)INFINITE) {
HS_ShowRect(m_hPlayer, nullptr);
}
SetRect(&m_rcZoom, 0, 0, m_stStreamInfo.nWidth, m_stStreamInfo.nHeight);
} else {
RECT rc = m_rcZoom, rcPrm = *pRc;
double fWidth = (double)fWndWidth / abs(m_rcZoom.left - m_rcZoom.right),
fHeight = (double)fWndHeight / abs(m_rcZoom.top - m_rcZoom.bottom);
fmtRect(rcPrm);
rc.left += (LONG)floor((double)rcPrm.left / fWidth);
rc.right = rc.left + (LONG)floor((double)abs(rcPrm.left - rcPrm.right) / fWidth);
rc.top += (LONG)floor((double)rcPrm.top / fHeight);
rc.bottom = rc.top + (LONG)floor((double)abs(rcPrm.top - rcPrm.bottom) / fHeight);
if (m_hPlayer != (void*)INFINITE) {
bool bRet = IsValidZoomRc(&rc) && 0 == HS_ShowRect(m_hPlayer, &rc); // 将要显示的区域传给播放库
if (bRet) {
m_rcZoom = rc;
}
}
}
}
}
// 鼠标滚轮缩放接口
void DoWheelZoom(POINT ptMouse, int wndWidth, int wndHeight, short zDelta) {
if (!m_bZoom || m_hPlayer == (void*)INFINITE) {
return;
}
// 计算缩放比例 - 每次放大20%或缩小25%
double scale = (zDelta > 0) ? 0.8 : 1.25;
// 当前视频显示区域的宽高
int currentWidth = m_rcZoom.right - m_rcZoom.left;
int currentHeight = m_rcZoom.bottom - m_rcZoom.top;
// 新的视频显示区域宽高
int newWidth = (int)(currentWidth * scale);
int newHeight = (int)(currentHeight * scale);
if (zDelta > 0) {
// 这里控制最多放大11次
double minWidth = m_stStreamInfo.nWidth * pow(scale, 12);
if (newWidth < minWidth) {
return;
}
} else {
// 这里控制只能缩小到视频原宽高
if (newWidth > m_stStreamInfo.nWidth ||
newHeight > m_stStreamInfo.nHeight) {
newWidth = m_stStreamInfo.nWidth;
newHeight = m_stStreamInfo.nHeight;
}
}
// 计算鼠标在窗口坐标系中的相对位置(0-1范围)
double mouseXRatio = ptMouse.x / (double)wndWidth;
double mouseYRatio = ptMouse.y / (double)wndHeight;
// 计算新的视频缩放区域，以鼠标位置为中心点
RECT rcNew = {};
int widthDiff = currentWidth - newWidth;
int heightDiff = currentHeight - newHeight;
rcNew.left = m_rcZoom.left + (int)(widthDiff * mouseXRatio);
rcNew.top = m_rcZoom.top + (int)(heightDiff * mouseYRatio);
rcNew.right = rcNew.left + newWidth;
rcNew.bottom = rcNew.top + newHeight;
// 确保不会超出视频边界
if (rcNew.left < 0) {
rcNew.right -= rcNew.left;
rcNew.left = 0;
}
if (rcNew.top < 0) {
rcNew.bottom -= rcNew.top;
rcNew.top = 0;
}
if (rcNew.right > m_stStreamInfo.nWidth) {
rcNew.left -= (rcNew.right - m_stStreamInfo.nWidth);
rcNew.right = m_stStreamInfo.nWidth;
}
if (rcNew.bottom > m_stStreamInfo.nHeight) {
rcNew.top -= (rcNew.bottom - m_stStreamInfo.nHeight);
rcNew.bottom = m_stStreamInfo.nHeight;
}
// 应用新的缩放区域
if (IsValidZoomRc(&rcNew)) {
HS_ShowRect(m_hPlayer, &rcNew);
m_rcZoom = rcNew;
}
}
// 拖拽画面接口
void DragMoveZoom(POINT ptMouse, int wndWidth, int wndHeight, bool bLBtnDown) {
if (!m_bZoom || m_hPlayer == (void*)INFINITE) {
return;
}
if (bLBtnDown) { // 鼠标左键按下事件
m_ptZoomDragStart = ptMouse;
m_rcZoomDragStart = m_rcZoom;
}
// 画面未处于放大状态，不支持拖拽
if (((m_rcZoom.right - m_rcZoom.left) == m_stStreamInfo.nWidth) &&
((m_rcZoom.bottom - m_rcZoom.top) == m_stStreamInfo.nHeight)) {
return;
}
// 计算鼠标移动的距离
int deltaX = m_ptZoomDragStart.x - ptMouse.x;
int deltaY = m_ptZoomDragStart.y - ptMouse.y;
// 根据窗口和实际视频的比例计算实际需要移动的距离
double scaleX = (double)(m_rcZoom.right - m_rcZoom.left) / wndWidth;
double scaleY = (double)(m_rcZoom.bottom - m_rcZoom.top) / wndHeight;
// 计算实际移动距离
int actualDeltaX = (int)(deltaX * scaleX);
int actualDeltaY = (int)(deltaY * scaleY);
// 计算新的显示区域
RECT rcNew = m_rcZoomDragStart;
rcNew.left += actualDeltaX;
rcNew.right += actualDeltaX;
rcNew.top += actualDeltaY;
rcNew.bottom += actualDeltaY;
// 边界检查
if (rcNew.left < 0) {
rcNew.right -= rcNew.left;
rcNew.left = 0;
}
if (rcNew.top < 0) {
rcNew.bottom -= rcNew.top;
rcNew.top = 0;
}
if (rcNew.right > m_stStreamInfo.nWidth) {
rcNew.left -= (rcNew.right - m_stStreamInfo.nWidth);
rcNew.right = m_stStreamInfo.nWidth;
}
if (rcNew.bottom > m_stStreamInfo.nHeight) {
rcNew.top -= (rcNew.bottom - m_stStreamInfo.nHeight);
rcNew.bottom = m_stStreamInfo.nHeight;
}
// 应用新的显示区域
if (IsValidZoomRc(&rcNew)) {
HS_ShowRect(m_hPlayer, &rcNew);
m_rcZoom = rcNew;
}
}
// ...省略其他代码
};
// 窗口类
class CPlayWnd {
// ...省略其他代码
private:
RECT m_arrBlock; // 记录框选的区域
bool m_bLBottonDowned; // 记录鼠标左键是否处于按下状态
int m_nWndWidth;
int m_nWndHeight;
public:
// 窗口事件响应函数
LRESULT ChildWinMsgProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam) {
switch (msg) {
// ...省略其他代码
case WM_LBUTTONDOWN: {
m_bLBottonDowned = true;
// SetCapture(hWnd); // 捕获鼠标
POINT ptMouse = { GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam) };
auto &rc = m_arrBlock;
rc.left = rc.right = LOWORD(lParam);
rc.top = rc.bottom = HIWORD(lParam);
/* 这里通知播放类CPlayer,调用到CPlayer的缩放和拖拽接口 */
/* OnDoZoom(m_nWndWidth, m_nWndHeight, &rc, false); */
/* OnDragZoom(m_nWndWidth, m_nWndHeight, ptMouse, true); */
} break;
case WM_MOUSELEAVE: {
if (m_bLBottonDowned) {
m_bLBottonDowned = false;
auto &rc = m_arrBlock;
/* 这里通知播放类CPlayer,调用到CPlayer的缩放接口 */
/* OnDoZoom(m_nWndWidth, m_nWndHeight, &rc, true); */
}
} break;
case WM_MOUSEMOVE: {
// 设置捕获鼠标离开窗口事件
TRACKMOUSEEVENT trackEvent;
trackEvent.cbSize = sizeof(TRACKMOUSEEVENT);
trackEvent.dwFlags = TME_LEAVE;
trackEvent.hwndTrack = hWnd;
TrackMouseEvent(&trackEvent);
if (m_bLBottonDowned) {
POINT ptMouse = { GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam) };
auto &rc = m_arrBlock;
rc.right = LOWORD(lParam);
rc.bottom = HIWORD(lParam);
/* 这里通知播放类CPlayer,调用到CPlayer的缩放和拖拽接口 */
/* OnDoZoom(m_nWndWidth, m_nWndHeight, &rc, false); */
/* OnDragZoom(m_nWndWidth, m_nWndHeight, ptMouse, false); */
}
} break;
case WM_MOUSEWHEEL: {
POINT ptMouse;
// 鼠标在屏幕的坐标
ptMouse.x = GET_X_LPARAM(lParam);
ptMouse.y = GET_Y_LPARAM(lParam);
// 转换为相对于窗口的坐标
ScreenToClient(hWnd, &ptMouse);
// 获取滚轮delta值
short zDelta = GET_WHEEL_DELTA_WPARAM(wParam);
/* 这里通知播放类CPlayer,调用到CPlayer的滚轮缩放接口 */
/* OnWheelZoom(ptMouse, m_nWndWidth, m_nWndHeight, zDelta); */
} break;
case WM_LBUTTONUP: {
if (m_bLBottonDowned) {
// ReleaseCapture(); // 释放鼠标捕获
m_bLBottonDowned = false;
auto &rc = m_arrBlock;
rc.right = LOWORD(lParam);
rc.bottom = HIWORD(lParam);
/* 这里通知播放类CPlayer,调用到CPlayer的缩放接口 */
/* OnDoZoom(m_nWndWidth, m_nWndHeight, &rc, true); */
}
} break;
case WM_RBUTTONUP: {
/* 这里通知播放类CPlayer,调用到CPlayer的缩放接口 */
/* OnDoZoom(0, 0, nullptr, true); */
} break;
case WM_LBUTTONDBLCLK: {
/* 这里通知播放类CPlayer,调用到CPlayer的缩放接口 */
/* OnDoZoom(0, 0, nullptr, true); */
} break;
// ...省略其他代码
}
}
// ...省略其他代码
};三、技术细节
- 本文主要介绍的是如何计算出显示区域，计算出来后将结果传给播放库去显示，播放库代码不在本文展示
- 使用
GET_X_LPARAM和GET_Y_LPARAM替代LOWORD和HIWORD处理坐标 - 正确处理屏幕坐标到客户区坐标的转换
- 不使用
SetCapture时，鼠标移出窗口后消息中断，拖动操作可能无法正常完成 - 使用
SetCapture后，可以跟踪整个拖动过程，即使鼠标移出窗口也能继续操作