Trapezoid Blt?

SpeedPear · #1 02-06-2004, 07:16 AM

I need to blt the image of a wall to a trapezoid. Trapezoids are not squares so bitblt and strechblt wont work. Any ideas?

Bljashinsky · #2 02-06-2004, 08:11 AM

I don't understand why bitblt won't work. Please enlighten me because as far as I know as long as you have a mask of an image any shape will work. I am sort of new to bitblt so I may be wrong.

Iceplug · #3 02-06-2004, 08:16 AM

Indeed, you should be able to draw a trapezoid picture of a wall with BitBlt... if you make a mask of a trapezoid, and then make a picture of the wall shaped like a trapezoid, then you can do it.

rpgnewbie · #4 02-06-2004, 01:28 PM

Quote:
Originally Posted by SpeedPear
I need to blt the image of a wall to a trapezoid. Trapezoids are not squares so bitblt and strechblt wont work. Any ideas?

Please check out "VB_Image Perspective.zip" attached to this thread:
http://www.xtremevbtalk.com/t114884.html

I use this program (which uses stretchblt) to "reshape" a square bitmap into a trapezoidal shape to create perspective mapped textured "walls" for a pseudo-3d maze game I made.

Attached are a couple of screenies of the program at design and run time to show that the "reshaping" happens at run time;

And personnally I would never start a thread with a post saying something "won't" work. It's better to say "I don't know how to get such and such to work..."

SpeedPear · #5 02-06-2004, 03:11 PM

RPG Newbie, thank you SO much. I still have a problem though.

. I need to repeatedly stretch the wall and bitblt it right inside the trapezoid. Your code seems to go off of a mask. Since the trapezoid always changes depending on angle, it would be impossible to have enough masks for it, unless I'm just not understanding your code. other than that, its exactly what I was looking for. I already know how to use bitblt, but needed to put a square onto a trapezoid. Others, thanks for trying...

Squalion · #6 02-06-2004, 03:21 PM

I think to do that, and have it changed depending on angle, you'd need to be using some form of DirectX. Well it'd be easier that way, than finding a huge workaround in gdi or win32.

SpeedPear · #7 02-06-2004, 03:29 PM

I AM going to do it in bitblt or some other form of API. I've tryed DirectX and it's not my cup of tea. I figure it won't be worth it. I mainly want to specify 4 x,y coordinates to the function and have it draw it. Of course there will be other parameters to this function that i will make. This is urgent in case you guys were wondering...

rpgnewbie · #8 02-06-2004, 05:21 PM

Quote:
Originally Posted by SpeedPear
I AM going to do it in bitblt or some other form of API. I've tryed DirectX and it's not my cup of tea. I figure it won't be worth it. I mainly want to specify 4 x,y coordinates to the function and have it draw it. Of course there will be other parameters to this function that i will make. This is urgent in case you guys were wondering...

Why is it that knee jerk response is so often DirectX. It's a great "tool", but you don't always have to use it for everything. (a hammer doesn't make a good screwdriver

)

Anyway, I think if you wise to be seeking another method if you have a lot of masks to generate (they can take up a lot of space).

Here is OnErrOr's Code Library thread to get you started with "programmatic" (on-the-fly) masking:
http://www.xtremevbtalk.com/t109862.html

SpeedPear · #9 02-06-2004, 05:53 PM

actually, i've generated masks during run time. of course this od can be VERY slow, if i'm correct, on error does it differently then I did. Generally, I'm very good at looking at code and then learning from it. However, I don't know anything about DCs and that stuff. I generally bitblt from picture boxes ect. Any ideas on how I can port this code to about a 20-30 function to generate masks quickly?

hDC_0 · #10 02-06-2004, 06:31 PM

Quote:
Originally Posted by SpeedPear
actually, i've generated masks during run time. of course this od can be VERY slow, if i'm correct, on error does it differently then I did. Generally, I'm very good at looking at code and then learning from it. However, I don't know anything about DCs and that stuff. I generally bitblt from picture boxes ect. Any ideas on how I can port this code to about a 20-30 function to generate masks quickly?

Hmmm, on one hand you are complaining about speed and the other you say you don't know much about "DCs and such"...

I guess I can only tell you that using MemoryDCs ARE the answer to any speed concerns. They are the fastest way that VB has to manipulate graphics short of DirectX.

So my "idea" about porting OnErrOr's code (to what you specifically want to do) is to just try getting it to do what you want. Maybe the learning curve for working with Device Contexts is not as steep as you think. If you run into difficulties, post the code that is giving you problems and someone (maybe even OnErrOr) will try to help...

I noticed your "Aeon Nexus" page has a link to "New World Games" - Are you doing this project in connection with Bljashinsky?

Rockoon · #11 02-06-2004, 09:29 PM

This falls under the texture mapping algorithms..

..the idea is rather simple to understand tho not so simple to code up and make everything work .. but given a 4-cornered polygon specified by 4 X/Y pairs -- its simply a matter of looping through all the pixels within this polygon and convert the pixels X/Y to the textures (bitmap) X/Y .. and grabbing the color for the pixel from it.

I've used the term 'simply' when really its not so simple until you understand it.. very detailed docs can be found on GameDev

The hard part isnt so much the texture mapping - the hard part is optimising it.

SpeedPear · #12 02-07-2004, 07:40 AM

I've started on something that goes pixel by pixel stretching it to the trapezoid with no luck. I have the basic concept on how to do it but for some reason I can't do it. About the site, BJashinsky's link is on it because I think he asked me to put it on it. I think that's how it was but I don't remember that well. He is not working on it. I guess you were also asking me that to know why I'm working on this instead of the RPG. The answer is that this game was a side project type deal. I guess it's time to start learning about Device Contexts and how to use them and take advantage of them for my programs. Do any of you know of a good tutorial to get me started?

SpeedPear · #13 02-07-2004, 06:12 PM

Anyone?

JimCamel · #14 02-07-2004, 07:16 PM

If you're doing it pixel by pixel, you could try something like this:

Code:

Private Declare Function GetPixel Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long) As Long
Private Declare Function SetPixel Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long, ByVal crColor As Long) As Long


Private Sub Command1_Click()
Dim i As Integer, j As Integer
Dim startx As Integer

For j = 0 To srcPicture.Height
    For i = 0 To srcPicture.Width
        SetPixel destPicture.hdc, i + startx, j, GetPixel(srcPicture.hdc, i, j)
    Next i
    startx = startx + 1
Next j
End Sub

All you need is an image in a picturebox called srcPicture, and a picturebox called destPicture which will be drawn in. If you want to change the slope, just change the value which you're adding to StartX each loop.

Bljashinsky · #15 02-07-2004, 07:19 PM

Here's a link to the MSDN page on device context's.
http://msdn.microsoft.com/library/de...vcons_0g6r.asp

rpgnewbie · #16 02-07-2004, 09:30 PM

On Lucky's gaming site there is an article (you might want to look at comparing times with different techinques: Pset/Point, GetPixel/SetPixel, GetPixel/SetPixel with DCs, and using Pointers:
http://www.rookscape.com/vbgaming/tutAY.php

I have spent many hours playing with the code on BillSoo's Tutor's Corner post dealing with Direct memory Access (DMA):
http://www.xtremevbtalk.com/t25347.html

There are many places on the Internet to learn about using Device Contexts with VB. Here's just a few:
http://www.officecomputertraining.co...ges/page44.asp
http://www.vb-helper.com/howto_memory_bitmap_text.html

and check out "Using and creating memory DCs" at the bottom of this page:
http://www.vbexplorer.com/VBExplorer/gdi2.asp

Note the MemoryDC sample mentioned on the page link above is part of a zip package "sam_pro.zip" which can be downloaded by clicking on "Download All Sample" link on this page:
http://www.vbexplorer.com/VBExplorer/gdi.asp

SpeedPear · #17 02-08-2004, 09:46 AM

Thank you all so much.