Pixel perfect question
Blitz3D Forums/Blitz3D Programming/Pixel perfect question
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| I have been looking through the pixel perfect code from the archives, but i can't pick out what part actually does the pixel perfect positioning/scaling. Don't think my head is screwed on right today. |
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| well it's pretty simple, you need to position a quad or sprite in front of the camera in a way that gives you the same amount of texels and pixels onscreen. If you once got that, you need to move the quad/sprite by a half pixel, because texels are centered, pixels are not. You should use a texture flag that turns off mipmapping to get a sharp texture, eg. flag 256. |
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| In my pixie code it is a magic pivot that they are parented to that provides the precision. |
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| Ross, The majic pivot in skidracers code confused me a bit so, a simpler way to get a texel's width on screen is initialising GUIsx, GUIsy with ... GUIplane = CreatePlane( 1, GUIcamera ) RotateEntity GUIplane, -90,0,0 PositionEntity GUIplane, 0,0,1 EntityPickMode GUIplane, 2 CameraPick ( GUIcamera, 0,0 ) sx# = PickedX() sy# = PickedY() CameraPick ( GUIcamera, 1,1 ) GUIsx# = PickedX() - sx GUIsy# = sy - PickedY() FreeEntity GUIplane Create quads like so ... Function GUI_Quad( sx#, sy#, Texture=0 , Free = False , ox#=0, oy#=0 , oz# = 0 , order=-998 ) mesh = CreateMesh( GUIcamera ) s = CreateSurface( mesh ) For iy = 0 To 1 For ix = 0 To 1 px# = ( ix * sx - ox ) * GUIsx py# = ( -iy * sy + oy ) * GUIsy AddVertex s, px, py, oz, ix+.5*(1.0/sx), iy+.5*(1.0/sy ) Next Next AddTriangle s, 0,1,3 AddTriangle s, 3,2,0 EntityFX mesh, 1 If Texture > 0 EntityTexture mesh , Texture If Free FreeTexture Texture EndIf EntityOrder mesh, order Return mesh End Function Then position with ..... Function GUI_Position( Entity , x#, y# ) PositionEntity Entity, ( x - HGW ) * GUIsx , ( HGH - y ) * GUIsy, 0 End Function Where HGW, HGH are half graphics width / height Stevie |
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| Ah, thanks stevie, that's more like it :o) |
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I always preferred mapping units to pixels/texels. If you move the camera back far enough (or your pixel-perfect pivot forward far enough) you don't need to do arithmetic when positioning quads:PositionEntity quad\entity, quad\x, quad\y, 0 Half of one, point five of the other. |
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| I got that working ;o) Tis very handy, as you can use, rects overlap to select the quads :o) |
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| I am lost. What are texels? What is Pixel Perfect? |
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| Ross, any chance of a look at the code? This may be a better option for me too ( rects overlap instead of camerapicks ) but not sure how you go about scaling so that 1 textel = 1 unit. Assume rects overlap allows the use of textures? Cheers Stevie |
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| Nope, all you do is get the x,y co-ord of the sprite/quad, stick in the width and height, and your sorted. This uses 1 pixel = 1 blitz unit. Thus your able to move the meshes, in 2d co-ords. The Y is inverted because of the 3d co-ords uses Y differently. www.rosscrooks.pwp.blueyonder.co.uk/editor1.zip |
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This part, from the "buttons.bb"
Global GUI_cam_piv = CreatePivot()
EntityParent GUI_cam_piv,camera
PositionEntity GUI_cam_piv,-1,0.75,1
Global GUI_texture = LoadTexture("images/icons.png")
Global GUI_mesh = CreateMesh()
Global GUI_surf = CreateSurface(GUI_mesh)
EntityParent GUI_mesh,GUI_cam_piv
PositionEntity GUI_mesh,0,0,0
ScaleEntity GUI_mesh,0.03125,0.03125,0.03125
EntityTexture GUI_mesh,GUI_texture
EntityFX GUI_mesh,1+2+32
EntityPickMode GUI_mesh,2
Global GUI_pm# = 0.0625 * (1024.0/gwidth)
Global GUI_quad_size# = 1024.0/gwidth
Global GUI_icon_size# = 32 ; the pixel size of the icons.
I've worked out the scalings. So, using that code... you add a quad by: add_quad(GUI_pm * b\x ,GUI_pm * -b\y,0,b\icon,0) The parameters use the variable GUI_pm, which, when multiplied by your pixel value, give the co-ords in 3d, where to place the quad. The Y is minus because your using 3d co-ords mind, but they equate to 2d co-ords. Now, this isn't 1 texel = 1 pixel. This is, 1 blitz unit, = 1 pixel. That's why the GUI_mesh is scaled. The last two parameters in that function are for choosing the texture co-ords, by passing an icon variable. The function will multiple that by 32, to get the image of the icon. Completely irrevant to what your wanting though :o) Oh and: Global GUI_quad_size# = 1024.0/gwidth This part simply works out the difference in size, for my icons to appear the same size, regardless of the resolution. It would be the same if you were trying to draw a rect the same size in different resolutions. The scaling was based on a screen size of 1024x768. Any questions on that code, feel free to post. |
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| Actually, if you just include the "buttons.bb" into your project and call the create_quad() function, it will return the first vertex, so you can store that and move it. You'll need to have the buttons image file though. I'll need to work on that to make it more generic. |
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| Thanks Ross .. I'll take a look. Looks mode complex than the method I use though. Cheers again Stevie |
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| Well most of it is just for the editor :o) |
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| What is Pixel Perfect? Please? |
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| Pixel perfect is when you align the texels of a texture (the pixels that make up the texture), to the pixels that make up the screen. So, th ewidth of a texel on screen, is the width of a pixel onscreen, so they match up perfectly, and you get a clear display. In my case, i'm using the term to describe the matching of 3d co-ords to 2d screen co-ords, by scaling the mesh to a certain size. |
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| Thanks, that makes scence. |
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| Umm, what's a texel? Is that a textured pixel, or something else? If it's the former, how is that different from your plain old garden-variety pixel? |
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| A texel is a pixel on a texture basically. If your texture was 128x128, it would have 128x128 texels on it :o) |
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