How to get the current view size for an image in Delphi 2009

问题

I wish to get the current size for an image being displayed with TImage, this object has the Proportional property set to True and is aligned to Client with main form. So, when resizing the form I wanna get the current size for that image, not canvas size neither real size for that image. Getting the current size I can show what's the percentage for current image size respect to real image size. Thanks in advance

回答1:

You can compare Image1.Picture.Width or .Height with Image1.Width or .Height.

To know if the image is streched proportional using the horizontal or vertical dimension, you should compare the ratio's of the two:

if Image1.Width/Image1.Height > Image1.Picture.Width/Image1.Picture.Height then 
  Result:=Image1.Picture.Width/Image1.Width
else
  Result:=Image1.Picture.Height/Image1.Height;

using a mathematical trick to convert the divisions into multiplications, you can avoid the conversions into float values, which also calculate a bit faster by using:

if Image1.Width*Image1.Picture.Height >Image1.Picture.Width*Image1.Height then

回答2:

I don't think there's a built-in way to do this. You may just have to calculate it. Something like this:

1. Get the height and width of the canvas.
2. Get the height and width of the image's Picture property.
3. Calculate the ratios of the Picture's dimensions to the canvas's dimensions.
4. Whichever of the two ratios is smaller is your percentage.

回答3:

Load this picture into a virtual TCanvas (or whatever) and then leave the property Proportional as False. Now you can retrieve the original size of the picture. If the image is usually very big, maybe you should use some external graphical libraries.

来源：https://stackoverflow.com/questions/1262023/how-to-get-the-current-view-size-for-an-image-in-delphi-2009