Video Signals And Timing: Difference between revisions

==== {{Anchor|C_PRIME ====}}

'''Todo C_PRIME ''' Equals 40

==== {{Anchor|M_PRIME ====}}

'''Todo M_PRIME ''' Equals 600

==== {{Anchor|CELL_GRAN_RND ====}}

:Cell granularity - the amount of pixels the timings should be aligned to. For example, a VGA uses horizontal timings in multiples of the character clock, each character being 8 (graphics and some text modes) or 9 (most text modes) pixels wide. For a VGA graphics mode, you'll want to supply 8 here because of that. Depending on your specific hardware, you supply either 8 or 1.

==== {{Anchor|MIN_PORCH_RND ====}}

:'''Todo''' Equals 1. Used to force at least one unit of blanking around the sync period in order to not confuse graphics hardware?

==== {{Anchor|MIN_V_SYNC_AND_BACK_PORCH ====}}

==== {{Anchor|MARGINS_REQUIRED ====}}

:The margins are used to add a visible black surrounding to the displayed picture. I assume small margins are intended to make sure the entire picture is still visible when the picture isn't perfectly centered on the screen.

:In theory it would be possible to use margins to simulate a small screen on a larger screen, or to simulate different aspect ratios perfectly. For example, if you were setting up a 640 * 480 video mode on a 16:10 display you could make the left and right margin 64 pixels each (with no top or bottom margins), so that it looks exactly the same as it would on a 4:3 display, rather than being stretched to fit. The opposite is also possible (e.g. displaying 16:10 video data on a 4:3 display with "letterboxing"). Unfortunately the GTF calculations don't actually support different sized left/right and top/bottom margins.

==== {{Anchor|MARGIN_PERCENT ====}}

:'''(Fixme: Percentage!)''' Amount of margins you want to have around your screen. VESA suggests a default of 1.8 to allow for screens that do not perfectly fit the image to the center.

==== {{Anchor|INTERLACE_REQUIRED ====}}

:There are two kinds of video modes, interlaced and progressive modes. Progressive modes display the full frame in one go, while interlaced modes display each other scanline in each run, taking two frames to render the complete picture. Normally, you don't want this, and several video cards don't support it, so you will normally want to supply '''false''' here.

==== {{Anchor|V_LINES ====}}

:Vertical resolution of the display you want. For a 640x480 resolution, supply 480.

==== {{Anchor|H_PIXELS ====}}

:Horizontal resolution of the display you want. For a 640x480 resolution, supply 640. Note that video cards will usually want this to be a multiple of eight because of [[#CELL_GRAN_RND|cell granularity]].

==== {{Anchor|REFRESH_RATE_REQUIRED ====}}

==== {{Anchor|V_LINES_RND ====}}

:Amount of active display scanlines per frame. Equals [[#V_LINES|the Y resolution]] unless interlaced modes are used.

==== {{Anchor|H_PIXELS_RND ====}}

:Actual horizontal resolution used. Basically contains [[#H_PIXELS|the X resolution]] rounded to the nearest allowed boundary.

==== {{Anchor|V_FIELD_RATE_REQUIRED ====}}

:Rate of complete images being sent to the monitor per second. Unless interlaced mode is used, equals the refresh rate.

==== {{Anchor|TOP_MARGIN_LINES ====}}

:Amount of margin at the top.

==== {{Anchor|BOTTOM_MARGIN_LINES ====}}

:Amount of margin at the bottom

==== {{Anchor|LEFT_MARGIN_PIXELS ====}}

:Amount of margin at the left

==== {{Anchor|RIGHT_MARGIN_PIXELS ====}}

:Amount of margin at the right