a question about the Rasterization Rules (Direct3D 10) page on MSDN

Discussion in '3D Hardware, Software & Output Devices' started by shuipi, Feb 22, 2010.

  1. shuipi

    Newcomer

    Joined:
    Mar 16, 2004
    Messages:
    73
    Likes Received:
    0
    Location:
    Beijing, China
    http://msdn.microsoft.com/en-us/library/ee415722(VS.85).aspx

    in the explanation under figure 1, it says "The dark gray covered pixels are examples of pixels that lie inside the triangle; the light gray colored pixels meet the top-left rule and are therefore drawn also."

    but from figure 1 it's obviously not the case, some pixels whose centers are right on a triangle edge are colored dark gray, while other pixels that are completely inside a triangle are colored light gray.

    Is there something fundamentally wrong with my understanding, or is the figure just completely screwed?
     
  2. LeGreg

    Newcomer

    Joined:
    Nov 1, 2003
    Messages:
    239
    Likes Received:
    3
    The dark and light pixels indicate to which triangle the pixel belongs to. So that if a pixel seems to be covered by two triangles in reality only one triangle determines if it's drawn or not.

    Eg : In the bottom right corner there are two triangle drawns, three pixels belongs to triangle on top but only one pixel belongs to triangle on bottom.
     
  3. Simon F

    Simon F Tea maker
    Moderator Veteran

    Joined:
    Feb 8, 2002
    Messages:
    4,560
    Likes Received:
    157
    Location:
    In the Island of Sodor, where the steam trains lie
    The second last pixel in the second last row surely is marked incorrectly.
     
  4. Axel

    Newcomer

    Joined:
    Dec 2, 2009
    Messages:
    2
    Likes Received:
    0
    Location:
    France
    Why ? It is part of the triangle on the right of the edge (since that is the triangle for which said edge is on the left), so it differs in color from the ones that are part of the triangle on the left of the edge.

    It gets trickier when a vertex aligns exactly with the pixel center. Looking at the picture, it looks like the pixel is covered iff the triangle has either 2 left edges or 1 left and 1 top at the vertex.
     
  5. Simon F

    Simon F Tea maker
    Moderator Veteran

    Joined:
    Feb 8, 2002
    Messages:
    4,560
    Likes Received:
    157
    Location:
    In the Island of Sodor, where the steam trains lie
    The legend reads:
    That dark grey pixel is on an edge so must be drawn according to a top-left rule and hence should be shaded light grey. <shrug>
     
  6. Jawed

    Legend

    Joined:
    Oct 2, 2004
    Messages:
    10,873
    Likes Received:
    767
    Location:
    London
    The legend isn't correct.

    In fact the pixels are shaded light or dark merely to indicate which triangle they belong to, in cases where two or more triangles form a mesh.

    Jawed
     
Loading...

Share This Page

  • About Us

    Beyond3D has been around for over a decade and prides itself on being the best place on the web for in-depth, technically-driven discussion and analysis of 3D graphics hardware. If you love pixels and transistors, you've come to the right place!

    Beyond3D is proudly published by GPU Tools Ltd.
Loading...