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193 lines
4.6 KiB
Plaintext
193 lines
4.6 KiB
Plaintext
VGI -- VMW Retro Vector Graphics Interface
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This was designed mostly as a proof-of-concept to drawing some Myst
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scenes. Might not work well for general graphics.
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The Apple II Hi-res screen is 280x192 and 6 colors with lots of limitations
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that are a bit complex to get into here. Some of the limitations in the
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interface here are working around Apple II issues.
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Apple II Hi-res Colors:
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~~~~~~~~~~~~~~~~~~~~~~~
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0 = black (for purple/green)
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1 = green
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2 = purple
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3 = white (for purple/green)
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4 = black (for blue/orange)
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5 = orange
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6 = blue
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7 = white (for blue/orange)
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Note Apple II uses NTSC artifact colors, so weird things happens when
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you try to put colors next to each other:
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+ Colors need to be two pixels wide, if you draw single width
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they may not appear depending on even/odd column
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+ White lines drawn single width will be colored instead
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+ Two colors of same group next to each other will have white or black
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border between
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+ Two colors of different group next to each other will have odd effects
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as can only change group every 3.5 pixels.
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The VGI Commands
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~~~~~~~~~~~~~~~~
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===================
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VGI Clearscreen (0)
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CLS color
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clears screen using ROM routine using color
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=================
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VGI Rectangle (1)
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RECT color1 color2 x1 y1 x2 y2
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draw filled rectangle from (x1,y1) to (x2,y2)
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color1 and color2 are drawn as alternating colors (horizontal stripes)
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x1 must be < 255. relative drawing is used so x2 can go to
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the edge of the screen (279)
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Unlike the other routines, this one uses custon horizontal-line
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routines for speed so much faster than the ROM line routine
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==============
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VGI Circle (2)
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CIRC color cx cy r
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Draw a circle of color with center (cx,cy) and radius r
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Circles with radius 0 will give an interesting non-circle effect.
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Bresenham circles are drawn and so certain sizes don't look the
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best. Also if the radius is too big things might break
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as the 8-bit unsigned int oveflows
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=====================
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VGI Filled Circle (3)
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FCIRC color cx cy r
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Draw a filled circle of color at location (cx,cy) with radius r
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=============
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VGI Point (4)
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POINT color x y
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Draws a point of color at (x,y)
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Note, X can be up to 279 here (the color is overloaded behind
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the scenes to support this)
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The last point you draw is the starting point for LINETO
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==============
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VGI Lineto (5)
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LINETO x y
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Draws a line to (x,y). The starting point and color come from
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the last POINT command.
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Note X cannot be > 255 so it can be trouble drawing at the right
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edge of the screen. POINT can go up to 279, so you might be able
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to get what you want by drawing from right to left
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==========================
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VGI Dithered Rectangle (6)
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DRECT c1 c2 x1 y1 x2 y2
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Draws a rectangle, but this time the two colors are raw bitmaps
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for the output colors, not one of the Apple II colors. This lets
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you do fancier dithered color patterns, but it's really hard
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getting dither patterns that look nice.
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=========================
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VGI Vertical Triangle (7)
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VTRI color vx vy xl xr yb
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VTRISK color vx vy xl xr yb skip
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Draw a flat bottom filled triangle of color.
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The top vertex is at (vx,vy)
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The bottom goes from (xl,yb) to (xr,yb)
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If your triangle is too tall you might get moire effects.
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This was much simpler than a proper filled triangle routine.
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The skip variant adds SKIP as an X increment instead of 1
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In memoy the skip is encoded in the high nibble of color
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===========================
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VGI Horizontal Triangle (8)
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HTRI color vx vy yt yb xr
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Draw a flat-sided filled triangle of color.
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The side vertex is at (vx,vy)
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The opposite side goes from (xr,yt) to (xr,yb)
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==================================
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VGI Vertical Striped Rectangle (9)
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VSTRP c1 c2 x1 y1 x2 y2
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Draws a rectangle, but this time the two colors are raw bitmaps
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for the output colors, but to use even/odd columns.
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On apple II this allows repeating pattern, but since it's a multiple
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of 7 you can't get true stripes (for that we'd need a 4-byte
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repeating pattern)
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=============
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VGI Line (10)
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LINE color x1 y1 x2 y2
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Draws a line from (x1,y1)
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Note, X1 can be up to 279 here (the color is overloaded behind
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the scenes to support this)
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The last point you draw is the starting point for LINETO
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=============
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VGI Line Far (11)
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LINE color x1 y1 x2 y2
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Draws a line from (x1,y1)
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In this one X2 must be > 255
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============
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VGI End (15)
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END
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this tells the drawing routine that we are done
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Size comparison:
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VGI data Captured+Compressed compressed autoconvert
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======== =================== ======================
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clock 385B 1228B
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rocket 623B
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door 189B
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book 212B
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firep 486B
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