Tuesday, March 3, 2020
Proportionally Resize an Image (TBitmap)
Proportionally Resize an Image (TBitmap) In graphics programming a thumbnail is a reduced-size version of a picture. Heres an idea for your next application: create a form picker to let users easily select and navigate through open forms by displaying thumbnails of them all in a dialog window. Interesting idea? Sounds like the Quick Tabs feature of the IE 7 browser :) Before actually creating such a neat feature for your next Delphi application, you need to know how to grab the image of the form (form-screen shot) and how to proportionally resize it to the desired thumbnail image. Proportional Picture Resizing: Creating Thumbnail Graphics Below you will find a block of code to take the image of a form (Form1) by using the GetFormImage method. The resulting TBitmap is then resized to fit the maximum thumbnail width (200 pixels) and/or height (150 pixels).Resizing maintains the aspect ratio of the image. The resulting image is then displayed in a TImage control, named Image1. const   maxWidth 200;   maxHeight 150; var   thumbnail : TBitmap;   thumbRect : TRect; begin   thumbnail : Form1.GetFormImage;   try     thumbRect.Left : 0;     thumbRect.Top : 0;     //proportional resize     if thumbnail.Width thumbnail.Height then     begin       thumbRect.Right : maxWidth;       thumbRect.Bottom : (maxWidth * thumbnail.Height) div thumbnail.Width;     end     else     begin       thumbRect.Bottom : maxHeight;       thumbRect.Right : (maxHeight * thumbnail.Width) div thumbnail.Height;     end;     thumbnail.Canvas.StretchDraw(thumbRect, thumbnail) ; //resize image     thumbnail.Width : thumbRect.Right;     thumbnail.Height : thumbRect.Bottom;     //display in a TImage control     Image1.Picture.Assign(thumbnail) ;   finally     thumbnail.Free;   end; end; Note: The GetFormImage only copies the form client area - if you need to take the entire screen shot of a form (including its border) youll need a different approach ...more about it next time.
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