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V1.1 March 2019
Video Settings
Scanlines
Mega Sg can generate simulated scanlines to
reproduce the scanning beam structure of a CRT.
Normal Scanlines dim pixels by the same amount
regardless of the pixel’s color. Hybrid Scanlines
targets more realistic scanlines by adjusting for
gamma when dimming a pixel’s color. With hybrid
scanlines, darker objects have thicker scanlines
than brighter objects.
In the opinion of many people, the thickness of
the scanlines produced in 720p modes is the ideal
thickness. This dims every third line. Scanlines in
1080p modes dim every fourth (4x-4.5x) or fifth (5x)
line. Some people view this as making the lines too
thin. Scalines in 480p mode dim every second line.
Some view these scanlines as too thick.
CRTs varied in their scanline thickness, with
higher quality displays tending to produce more
pronounced scanlines.
If you use scanlines, you may need adjust the
Vertical Position in the Width and Height from
the current setting to allow the scanlines to align
themselves with the top or bottom edge of each
line of scaled pixels. Having scanlines bisect a
scaled pixel is not ideal.
Extra Features
The Genesis/Mega Drive would show colored
borders on all four sides of the active display
area in many games. NTSC CRTs would typically
mask off most of these borders behind the
screen bezel, but PAL CRTs usually showed at least
some of the top and bottom borders.
Mega Sg can simulate this effect if you wish
by turning off the masking for the top and
bottom or left and right borders. The Genesis/
Mega Drive would also show colorful
flickering dots in the vertical borders which
represented entries into Color RAM, but the
Mega Sg does not simulate this artifact.
Dithering was a commonly used technique on
the Genesis/Mega Drive to blend colors of
adjacent pixels. With an RGB display, the pixels
would appear distinct and usually be in
a pattern of alternating vertical lines or a
checkerboard pattern where the pixels shift by
one every scanline. However, most people played
Genesis/Mega Drive through composite or RF
video. Composite video lacks the bandwidth to
show all pixels distinctly and will tend to blend
alternating patterns of two colored pixels.
Sometimes this was used as for transparency,
other times it would be used to show a mixed
color using the color directly generated by the
console. The slider will adjust the detection Mega
Sg uses to determine whether to blend
pixels or not.
Buffer Mode
The buffering modes on Mega Sg address the issue
that the Genesis/Mega Drive’s native NTSC frame
rate is 59.92275fps and the PAL rate is 49.70146fps.
A CRT can display these frame rates with ease but
modern displays and HDMI interfaces expect either
60fps. 59.94fps or 50fps and are generally not
tolerant of refresh rates that vary
from too far from the official frame rates.
Mega Sg has three modes that deal with the frame
rate differential in different ways.
Fully Buffered Mode buffers full frames to maintain
the timing of a 59.92 frame rate using only 60fps.
This mode avoids tearing at the cost of latency.
Mega Sg must render at least 1 frame ahead
of the game’s internal rendering to stay ahead.
Zero Delay Mode speeds Mega Sg up to achieve
a true 60fps frame rate, a speed difference of
0.13%. There is no latency penalty with this method
but this method causes Mega Sg to jump ahead by
about 1 second every 10 minutes compared to
an original Genesis/Mega Drive.
Single Buffer Mode is something of a compromise
between the two methods described above.
Like the Full Buffer option, the original timing is
being generated within Mega Sg. Unlike the Full
Buffer, only a portion of the next frame is being pre-
rendered, giving latency of no more than 1 frame
depending on when the player activates an input.
The drawback is a recurring retrace line that is
visible once per every several seconds.
