Perspective Shadows Help
 
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  1. #1
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    Perspective Shadows Help

    Hi guys.

    I'm trying to understand perspective shadow. I read the Perspective Made Easy book and it seems straight forward but when I try to do a simple box shadow, it seems odd:

    Name:  perspective_shadows.png
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    I can't see where I should "end" the shadow length, is the shadow above correct or should the shadow be enclosed within the aqua polygon ?

    Also sunlight is apparently "parallel". When I try to draw parallel rays of light, it makes it harder to tell where the shadow should end, is this the correct location?:

    Name:  perspective_shadows_sunlight.png
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    Can someone shed some light on this please? (no pun intended lol)

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  3. #2
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    Your construction is incomplete. You need to drop your sun on the horizon, and draw rays from the dropped sun through all ground vertices of the cube. Intersect these rays with the rays you already have to find the shadows of the vertices.

    Grinnikend door het leven...
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    Ahhhhh.

    That's how you do it, thanks.

    I swear the book was so subtle about it, it didn't even mention about drawing lines from the base of the point light source

    So what about sun light rays that are parallel, do we do the same? Drop a line down from the sun to the horizon, then draw through all 4 corners of the box base?

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    Quote Originally Posted by chewedon View Post
    So what about sun light rays that are parallel, do we do the same?
    Forget about parallel sun light rays. The sun is seen as a light source at infinite distance, so it is used as a vanishing point from which all light rays emerge...

    Grinnikend door het leven...
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    Alright, thanks for the pointers.

    It is less frustrating now

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  8. #6
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    here's an image to help you with the idea eezacque mentioned

    Name:  perspective of shadows.jpg
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    Quote Originally Posted by dpaint View Post
    here's an image to help you with the idea eezacque mentioned

    Name:  perspective of shadows.jpg
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    Thanks for the extra reference material dpaint.

    After eezacque told me to drop a line down from the light source to the horizon line and draw through all four corners of the box base, the lines finally intercepted and I was able to connect the dots...literally

    That circle box plane is very helpful. I was wondering how the book author know where to draw the ball shadow elongated as he projected the ball's shadow on a vertical standing wall.

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    This site should answer all of your shadow questions and there are diagrams to help with the concepts.
    http://handprint.com/HP/WCL/perspect6.html#shadowform

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  11. #9
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    Quote Originally Posted by chewedon View Post
    Ahhhhh.

    That's how you do it, thanks.

    I swear the book was so subtle about it, it didn't even mention about drawing lines from the base of the point light source

    So what about sun light rays that are parallel, do we do the same? Drop a line down from the sun to the horizon, then draw through all 4 corners of the box base?
    As Eezacque pointed out, they should all go towards the same shadow vanishing point on the horizon.

    If, however, you're talking about when the light source is to the side, you don't use a shadow vanishing point. You draw one arbitrary line through the top of one corner, and then the bottom of that corner, you just draw a straight line going right/left/whatever, and it'll join up with the first line. Then you copy those arbitrary lines for the other corners, and do the same straight lines at the bottom of those shapes.

    Does that make sense?

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  12. #10
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    Yes. I do recall that image from the book.

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