Video Signals And Timing: Difference between revisions
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Quick explanation of margins.. |
added more vars, removed round(x, 0) constructs |
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The formula's provided by VESA use various scales of constants. Brendan's working on changing the scales to units. Right now, the scale space is still unknown. |
The formula's provided by VESA use various scales of constants. Brendan's working on changing the scales to units. Right now, the scale space is still unknown. |
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== |
== Common parts of the GTF formulas == |
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<tt>[[#H_PIXELS_RND|H_PIXELS_RND]] = ( ''ROUND'' ( [[#H_PIXELS|H_PIXELS]] / [[#CELL_GRAN_RND|CELL_GRAN_RND]] ) ) * [[#CELL_GRAN_RND|CELL_GRAN_RND]] |
<tt>[[#H_PIXELS_RND|H_PIXELS_RND]] = ( ''ROUND'' ( [[#H_PIXELS|H_PIXELS]] / [[#CELL_GRAN_RND|CELL_GRAN_RND]] ) ) * [[#CELL_GRAN_RND|CELL_GRAN_RND]] |
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{<br /> |
{<br /> |
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:[[#V_LINES_RND|V_LINES_RND]] = ''ROUND'' ( [[#V_LINES|V_LINES]] / 2 )<br /> |
:[[#V_LINES_RND|V_LINES_RND]] = ''ROUND'' ( [[#V_LINES|V_LINES]] / 2 )<br /> |
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:[[#V_FIELD_RATE_REQUIRED|V_FIELD_RATE_REQUIRED]] = [[#REFRESH_RATE_REQUIRED| |
:[[#V_FIELD_RATE_REQUIRED|V_FIELD_RATE_REQUIRED]] = [[#REFRESH_RATE_REQUIRED|REFRESH_RATE_REQUIRED]] * 2<br /> |
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:[[#INTERLACE|INTERLACE]] = 0.5<br /> |
:[[#INTERLACE|INTERLACE]] = 0.5<br /> |
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} '''else''' {<br /> |
} '''else''' {<br /> |
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:[[#V_LINES_RND]] = ''ROUND'' ( [[#V_LINES]]) )<br /> |
:[[#V_LINES_RND|V_LINES_RND]] = ''ROUND'' ( [[#V_LINES|V_LINES]]) )<br /> |
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:[[#V_FIELD_RATE_REQUIRED]] = [[#REFRESH_RATE_REQUIRED]]<br /> |
:[[#V_FIELD_RATE_REQUIRED|V_FIELD_RATE_REQUIRED]] = [[#REFRESH_RATE_REQUIRED|REFRESH_RATE_REQUIRED]]<br /> |
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:[[#INTERLACE]] = 0<br /> |
:[[#INTERLACE|INTERLACE]] = 0<br /> |
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}<br /> |
}<br /> |
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'''if''' ( [[#MARGINS_REQUIRED]] == '''true''' ) {<br /> |
'''if''' ( [[#MARGINS_REQUIRED]] == '''true''' ) {<br /> |
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:[[#TOP_MARGIN_LINES]] = ''ROUND'' ( [[#MARGIN_PRECENT]] / 100 * [[#V_LINES_RND]] )<br /> |
:[[#TOP_MARGIN_LINES|TOP_MARGIN_LINES]] = ''ROUND'' ( [[#MARGIN_PRECENT]] / 100 * [[#V_LINES_RND]] )<br /> |
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:[[#BOTTOM_MARGIN_LINES]] = ''ROUND'' ( [[#MARGIN_PRECENT]] / 100 * [[#V_LINES_RND]] )<br /> |
:[[#BOTTOM_MARGIN_LINES|BOTTOM_MARGIN_LINES]] = ''ROUND'' ( [[#MARGIN_PRECENT]] / 100 * [[#V_LINES_RND]] )<br /> |
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:[[#LEFT_MARGIN_PIXELS]] = ( ''ROUND'' |
:[[#LEFT_MARGIN_PIXELS|LEFT_MARGIN_PIXELS]] = ( ''ROUND'' ( [[#H_PIXELS_RND]] * [[#MARGIN_PRECENT]] / 100 / [[#CELL_GRAN_RND]] ) ) * [[#CELL_GRAN_RND]]<br /> |
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:[[#RIGHT_MARGIN_PIXELS]] = ( ''ROUND'' |
:[[#RIGHT_MARGIN_PIXELS|RIGHT_MARGIN_PIXELS]] = ( ''ROUND'' ( [[#H_PIXELS_RND]] * [[#MARGIN_PRECENT]] / 100 / [[#CELL_GRAN_RND]] ) ) * [[#CELL_GRAN_RND]]<br /> |
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} '''else''' {<br /> |
} '''else''' {<br /> |
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:[[#TOP_MARGIN_LINES]] = 0<br /> |
:[[#TOP_MARGIN_LINES|TOP_MARGIN_LINES]] = 0<br /> |
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:[[#BOTTOM_MARGIN_LINES]] = 0<br /> |
:[[#BOTTOM_MARGIN_LINES|BOTTOM_MARGIN_LINES]] = 0<br /> |
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:[[#LEFT_MARGIN_PIXELS]] = 0<br /> |
:[[#LEFT_MARGIN_PIXELS|LEFT_MARGIN_PIXELS]] = 0<br /> |
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:[[#RIGHT_MARGIN_PIXELS]] = 0<br /> |
:[[#RIGHT_MARGIN_PIXELS|RIGHT_MARGIN_PIXELS]] = 0<br /> |
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}</tt> |
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} |
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== GTF Using resolution and refresh rate == |
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<tt> |
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[[#H_PERIOD_ESTIMATE]] = ( 1 / [[#V_FIELD_RATE_REQUIRED]] - [[#MIN_V_SYNC_AND_BACK_PORCH]] / 1000000 ) |
[[#H_PERIOD_ESTIMATE]] = ( 1 / [[#V_FIELD_RATE_REQUIRED]] - [[#MIN_V_SYNC_AND_BACK_PORCH]] / 1000000 ) |
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:/ ( [[#V_LINES_RND]] + 2 * [[#TOP_MARGIN_LINES]] + [[#MIN_PORCH_RND]] + [[#INTERLACE]] ) * 1000000 |
:/ ( [[#V_LINES_RND]] + 2 * [[#TOP_MARGIN_LINES]] + [[#MIN_PORCH_RND]] + [[#INTERLACE]] ) * 1000000 |
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==== CELL_GRAN_RND ==== |
==== CELL_GRAN_RND ==== |
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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. |
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. |
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| ⚫ | |||
'''Todo''' Equals 1.8 |
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==== MIN_PORCH_RND ==== |
==== MIN_PORCH_RND ==== |
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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. |
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. |
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| ⚫ | |||
(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. |
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==== INTERLACE_REQUIRED ==== |
==== INTERLACE_REQUIRED ==== |
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==== H_PIXELS ==== |
==== H_PIXELS ==== |
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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]]. |
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]]. |
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==== REFRESH_RATE_REQUIRED ==== |
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==== V_LINES_RND ==== |
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Amount of active display scanlines per frame. Equals [[#V_LINES|the Y resolution]] unless interlaced modes are used. |
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==== H_PIXELS_RND ==== |
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Actual horizontal resolution used. Basically contains [[#H_PIXELS|the X resolution]] rounded to the nearest allowed boundary. |
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==== V_FIELD_RATE_REQUIRED ==== |
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Rate of complete images being sent to the monitor per second. Unless interlaced mode is used, equals the refresh rate. |
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==== TOP_MARGIN_LINES ==== |
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Amount of margin at the top. |
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==== BOTTOM_MARGIN_LINES ==== |
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Amount of margin at the bottom |
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==== LEFT_MARGIN_PIXELS ==== |
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Amount of margin at the left |
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==== RIGHT_MARGIN_PIXELS ==== |
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Amount of margin at the right |
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= Brendan's Original Posts = |
= Brendan's Original Posts = |
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