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[英]How to color blend (colorize by specified alpha value) the canvas area using pure GDI?
[英]How to change a color in an area of a canvas
我試圖在TCanvas上單擊並拖動,並在向下拖動時將背景顏色更改為clHighlight,如果要反轉拖動方向,則將其更改回clWhite。 如果您單擊您正在閱讀的文本並向下或向上拖動,無論如何都會發生幾乎所有的事情。 我已經從這個鏈接中收集了
自從我第一次發布此代碼以來,我已經對下面的代碼進行了廣泛的編輯,下面的代碼現在可以執行我打算要做的事情,除了如果您不以均勻的速度拖動時所選內容中的文本可能會弄亂,這就是不能接受的。 如果您確實真正快速地上下移動鼠標,則肯定會弄亂它。 如果您以穩定的速度移動鼠標,則效果很好,這使我擔心可能無法解決該問題。 如果有人有什么好建議,我會繼續研究。 我還遇到了幾個“資源不足”錯誤,不確定是怎么回事,我正在釋放位圖,沒有其他我知道的資源參與其中。
以下代碼位於MouseMove事件中。srect是TImage畫布中的選定矩形。 drect與轉換為0,0的相同srect。 bm1包含使用CopyRect從TImage的畫布復制的選定矩形。 bm2包含bm1,並且使用BrushCopy將clWhite(背景)更改為clHighlight(或相反)。 然后使用BitBlt將bm2復制回原始TImage的選定矩形。
// vp is derived from TImage
if (Y > sel_data->_last_y)
{
TRect srect = Rect(sel_data->_rect.Left,sel_data->_last_y,sel_data->_rect.Right, Y);
TRect drect = Rect(sel_data->_rect.Left,0,sel_data->_rect.Right, sel_data->_rect.Height() - 1);
Graphics::TBitmap* bm1 = new Graphics::TBitmap;
bm1->Width = srect.Width();
bm1->Height = srect.Height();
Graphics::TBitmap* bm2 = new Graphics::TBitmap;
bm2->Width = srect.Width();
bm2->Height = srect.Height();
bm1->Canvas->CopyRect(drect, vp->Canvas, srect);
bm2->Canvas->Brush->Color = clHighlight;
bm2->Canvas->BrushCopy(drect, bm1, drect, clWindow);
BitBlt(vp->Canvas->Handle, srect.Left, srect.Top, srect.Width(), srect.Height(),
bm2->Canvas->Handle, 0, 0, SRCCOPY);
vp->Refresh();
delete bm1;
delete bm2;
}
else if (Y < sel_data->_last_y)
{
TRect srect = Rect(sel_data->_rect.Left, Y,sel_data->_rect.Right, sel_data->_last_y);
TRect drect = Rect(sel_data->_rect.Left,0,sel_data->_rect.Right, sel_data->_rect.Height() - 1);
Graphics::TBitmap* bm1 = new Graphics::TBitmap;
bm1->Width = srect.Width();
bm1->Height = srect.Height();
Graphics::TBitmap* bm2 = new Graphics::TBitmap;
bm2->Width = srect.Width();
bm2->Height = srect.Height();
bm1->Canvas->CopyRect(drect, vp->Canvas, srect);
bm2->Canvas->Brush->Color = clWhite;
bm2->Canvas->BrushCopy(drect, bm1, drect, clHighlight);
int w = srect.Width();
int h = srect.Height();
BitBlt(vp->Canvas->Handle, srect.Left, srect.Top, w, h, bm2->Canvas->Handle, 0, 0, SRCCOPY);
vp->Refresh();
delete bm1;
delete bm2;
}
sel_data->_last_y = Y;
}
這就是我最終得到的結果,據我所知,所有故障均已修復,其中包括整個MouseMove事件處理程序。 上面提到的鏈接使我很困惑,因為我需要一個CopyRect,一個BrushCopy和一個BitBlt。
void __fastcall Tviewer_ui::viewerPageMouseMove(TObject *Sender, TShiftState Shift, int X, int Y)
{
if (_selecting)
{
TColor to_color = 0;
TColor from_color = 0;
Tviewer_page* vp = static_cast<Tviewer_page *>(Sender);
Tsel_data* sel_data = &vp->_sel_datas[vp->_c_sel];
// Scroll window if needed
int sb_pos = _scrollBox->VertScrollBar->Position;
if (Y > sb_pos - vp->_top + _scrollBox->Height - 10)
_scrollBox->VertScrollBar->Position += 10;
else
if (Y < sb_pos - vp->_top + 10)
_scrollBox->VertScrollBar->Position -= 10;
int y1 = 0;
int y2 = 0;
if (Y > sel_data->_start_y)
{
if (Y > sel_data->_last_y)
{
y1 = sel_data->_last_y;
y2 = Y;
from_color = clWhite;
to_color = clHighlight;
}
else if (Y < sel_data->_last_y)
{
y1 = Y;
y2 = sel_data->_last_y;
from_color = clHighlight;
to_color = clWhite;
}
sel_data->_rect.Bottom = Y;
}
else if (Y < sel_data->_start_y)
{
if (Y < sel_data->_last_y)
{
y1 = Y;
y2 = sel_data->_last_y;
from_color = clWhite;
to_color = clHighlight;
}
else if (Y > sel_data->_last_y)
{
y1 = sel_data->_last_y;
y2 = Y;
from_color = clHighlight;
to_color = clWhite;
}
sel_data->_rect.Top = Y;
}
int height = abs(y1 - y2);
if (height > 0)
{
TRect srect = Rect(sel_data->_rect.Left, y1, sel_data->_rect.Right, y2);
int width = srect.Width();
TRect drect = Rect(sel_data->_rect.Left,0,sel_data->_rect.Right, height);
Graphics::TBitmap* bm1 = new Graphics::TBitmap;
bm1->Width = width;
bm1->Height = height;
Graphics::TBitmap* bm2 = new Graphics::TBitmap;
bm2->Width = width;
bm2->Height = height;
bm1->Canvas->CopyRect(drect, vp->Canvas, srect);
bm2->Canvas->Brush->Color = to_color;
bm2->Canvas->BrushCopy(drect, bm1, drect, from_color);
BitBlt(vp->Canvas->Handle, srect.Left, srect.Top, width, height, bm2->Canvas->Handle, 0, 0, SRCCOPY);
vp->Refresh();
delete bm1;
delete bm2;
}
sel_data->_last_y = Y;
}
}
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