Graphics Minterms - Revision history

Steven Solie at 22:13, 28 September 2015

2015-09-28T22:13:09Z

← Older revision		Revision as of 22:13, 28 September 2015
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	\| 1 \|\| 1 \|\| 1 \|\| ? \|\| 7 \|\| ABC		\| 1 \|\| 1 \|\| 1 \|\| ? \|\| 7 \|\| ABC
	\|}		\|}

	Where 'N' represents 'not'.

	This information is collected in a standard format, the LF (Logic Function) control byte in the BLTCON0 register. This byte programs the blitter to perform one of the 256 possible logic operations on three sources for a given blit.		This information is collected in a standard format, the LF (Logic Function) control byte in the BLTCON0 register. This byte programs the blitter to perform one of the 256 possible logic operations on three sources for a given blit.
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	would fill in the last four entries of the truth table with 1 (because the A bit is set) and the third, fourth, seven, and eight entries with 1		would fill in the last four entries of the truth table with 1 (because the A bit is set) and the third, fourth, seven, and eight entries with 1
	(because the B bit is set), and all others (the first and second) with 0, because neither A nor B is set. Then, we read the truth table from the		(because the B bit is set), and all others (the first and second) with 0, because neither A nor B is set. Then, we read the truth table from the
	bottom up, reading 11111100, or ~~$FC~~.		bottom up, reading 11111100, or 0xFC.

	For another example, an LF control byte of ~~$80~~ ( = 1000 0000 binary) turns on bits only for those points of the D destination rectangle where the		For another example, an LF control byte of 0x80 (= 1000 0000 binary) turns on bits only for those points of the D destination rectangle where the
	corresponding bits of A, B, and C sources were all on (ABC = 1, bit 7 of LF on). All other points in the rectangle, which correspond to other combinations for A, B, and C, will be 0. This is because bits 6 through 0 of the LF control byte, which specify the D output for these situations,		corresponding bits of A, B, and C sources were all on (ABC = 1, bit 7 of LF on). All other points in the rectangle, which correspond to other combinations for A, B, and C, will be 0. This is because bits 6 through 0 of the LF control byte, which specify the D output for these situations,
	are set to 0.		are set to 0.

Steven Solie at 22:06, 28 September 2015

2015-09-28T22:06:36Z

← Older revision		Revision as of 22:06, 28 September 2015
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	! LF code (minterm)		! LF code (minterm)
	! Logic operation performed during copy		! Logic operation performed during copy
⚫	\|-
⚫	\| D = A + B
⚫	\| 0xC0
⚫	\| Copy from source to destination.
	\|-		\|-
	\| D = A + NB		\| D = A + NB
	\| 0x30		\| 0x30
	\| Replace destination area with inverted source.		\| Replace destination area with inverted source.
⚫	\|-
⚫	\| D = A + B + C
⚫	\| 0xE0
⚫	\| Copy from source to destination through mask
	\|-		\|-
	\| D = A + NC		\| D = A + NC
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	\| Replace destination area with an inverted version of itself.		\| Replace destination area with an inverted version of itself.
	\|-		\|-
	\| D = A + (B + ~~NC)(NB + C)~~		\| D = A + BNC + NBC
	\| 0x60		\| 0x60
	\| Put source where the mask is not, put the mask where the source is not (cookie cut).		\| Put source where the mask is not, put the mask where the source is not (cookie cut).
	\|-		\|-
	\| D = A + ~~B + D~~		\| D = A + BC
	\| 0x80		\| 0x80
	\| Only put bits into destination where there is a bit in the same position for both source and destination (sieve operation).		\| Only put bits into destination where there is a bit in the same position for both source and destination (sieve operation).
		⚫	\|-
		⚫	\| D = A + B
		⚫	\| 0xC0
		⚫	\| Copy from source to destination.
		⚫	\|-
		⚫	\| D = A + B + C
		⚫	\| 0xE0
		⚫	\| Copy from source to destination through mask
	\|}		\|}

Steven Solie at 21:59, 28 September 2015

2015-09-28T21:59:53Z

← Older revision		Revision as of 21:59, 28 September 2015
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	Here is a table of the most often used graphics blitter logic functions and what they do:		Here is a table of the most often used graphics blitter logic functions and what they do:
	{\| class="wikitable"		{\| class="wikitable"
	! ~~Selected~~ equation		! Logic equation
	! LF code (minterm)		! LF code (minterm)
			! Logic operation performed during copy
	! Description
	\|-		\|-
	\| D = A + B		\| D = A + B
	\| 0xC0		\| 0xC0
	\| Copy from source to destination		\| Copy from source to destination.
	\|-		\|-
	\| D = A + NB		\| D = A + NB
	\| 0x30		\| 0x30
			\| Replace destination area with inverted source.
	\| Invert source before copy
	\|-		\|-
	\| D = A + B + C		\| D = A + B + C
	\| 0xE0		\| 0xE0
	\| Copy from source to destination through mask		\| Copy from source to destination through mask
			\|-
			\| D = A + NC
			\| 0x50
			\| Replace destination area with an inverted version of itself.
			\|-
			\| D = A + (B + NC)(NB + C)
			\| 0x60
			\| Put source where the mask is not, put the mask where the source is not (cookie cut).
			\|-
			\| D = A + B + D
			\| 0x80
			\| Only put bits into destination where there is a bit in the same position for both source and destination (sieve operation).
	\|}		\|}

			{{Note\|The logic equations only make sense when you know what the four channels are assigned to as explained below.}}

	Some background knowledge of the classic Amiga blitter hardware is helpful to understand how to derive the minterm argument and decode what it means.		Some background knowledge of the classic Amiga blitter hardware is helpful to understand how to derive the minterm argument and decode what it means.

Steven Solie at 21:38, 28 September 2015

2015-09-28T21:38:29Z

Show changes

Steven Solie: /* Designing the LF Control Byte with Minterms */

2015-09-28T21:22:04Z

Designing the LF Control Byte with Minterms

← Older revision		Revision as of 21:22, 28 September 2015
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	The wide range of logic operations allow some sophisticated graphics techniques. For instance, you can move the image of a car across some pre-existing building images with a few blits. Producing this effect requires predrawn images of the car, the buildings (or background), and a		The wide range of logic operations allow some sophisticated graphics techniques. For instance, you can move the image of a car across some pre-existing building images with a few blits. Producing this effect requires predrawn images of the car, the buildings (or background), and a
	car "mask" that contains bits set wherever the car image is not transparent. This mask can be visualized as the shadow of the car from a light source at the same position as the viewer.		car "mask" that contains bits set wherever the car image is not transparent. This mask can be visualized as the shadow of the car from a light source at the same position as the viewer.

	Table 6-1 lists some of the most common functions and their values, for
	easy reference.

	Table 6-1: Table of Common Minterm Values


	Selected BLTCON0 Selected BLTCON0
	Equation LF Code Equation LF Code
	-------- ------- -------- -------
	D = A $F0 D = AB $C0
	_ _
	D = A $0F D = AB $30
	_
	D = B $CC D = AB $0C
	_ __
	D = B $33 D = AB $03

	D = C $AA D = BC $88
	_ _
	D = C $55 D = BC $44
	_
	D = AC $A0 D = BC $22
	_ __
	D = AC $50 D = AC $11
	_ _
	D = AC $0A D = A + B $F3
	_ _ _
	D = AC $05 D = A + B $3F
	_
	D = A + B $FC D = A + C $F5
	_ _ _
	D = A + B $CF D = A + C $5F
	_
	D = A + C $FA D = B + C $DD
	_ _ _
	D = A + C $AF D = B + C $77
	_
	D = B + C $EE D = AB + AC $CA
	_
	D = B + C $BB

Steven Solie at 21:21, 28 September 2015

2015-09-28T21:21:41Z

Steven Solie: /* Creating Logic Functions */

2015-09-28T21:19:33Z

Creating Logic Functions

@@ Line 79: / Line 79: @@
 This means only the upper 4 bits (bits 4 to 7) of the minterm are used to select the logic operation. The lower bits (0 to 3) will always be zero because channel A is always non-zero or inside the rectangle.
-= Creating Logic Functions =
+= Creating Graphics Logic Functions =
-Creating your own logic functions is easy if you understand there are four channels (A, B, C, D) and what each channel is assigned to do.
+Creating your own graphics logic functions is easier if you understand there are four channels (A, B, C, D) and what each channel is assigned to do.
-== Select channel A ==
+'''1. Select channel A'''
-With all of the graphics.library functions channel A is non-zero only when inside the rectangle. This ensures that all pixels outside the rectangle are ignored for purposes of the blit. There is no other choice for channel A.
+With all of the graphics.library functions, channel A is non-zero only when inside the rectangle. This ensures that all pixels outside the rectangle are ignored for purposes of the blit. There is no other choice for channel A.
-== Select channel B ==
+'''2. Select channel B'''
 Channel B is always the source rectangle. You may choose to select pixels as-is (B) or invert them as they are read from the source (NB).
-== Select channel C ==
+'''3. Select channel C'''
 Channel C is either a mask the same dimensions as the channel B source rectangle or it is not used and defined as the destination. When used as a mask, you can choose to select pixels in the mask (C) or not in the mask (NC).
-== Determine channel D logic function ==
+'''4. Determine logic function'''
-Channel D is always the destination channel.
+Channel D is always the destination channel. Select a logic function to perform using channel D as the destination.
 = Designing the LF Control Byte with Minterms =

Steven Solie: /* Graphics Minterms */

2015-09-28T20:11:43Z

Graphics Minterms

← Older revision		Revision as of 20:11, 28 September 2015
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	are set to 0.		are set to 0.

	= Graphics ~~Minterms~~ =		= Graphics Logic Functions =

	The blitter functions provided by graphics.library were originally designed to support the classic Amiga blitter with a total of 4 DMA channels. Modern graphics cards have their own blitter(s) which programmers are not allowed direct access to. However, the minterm value still exists to help specify logic operations to perform while performing the copy which may or may not be assisted by the graphics card hardware.		The original blitter functions provided by graphics.library like BltBitMap() were originally designed to support the classic Amiga blitter with a total of 4 DMA channels. Modern graphics cards have their own blitter(s) which programmers are not allowed direct access to. However, the minterm value still exists to help specify logic operations to perform while performing the copy which may or may not be assisted by the graphics card hardware.

	The roles of each of the 4 channels are as follows:		The roles of each of the 4 channels are as follows:

Steven Solie: /* Creating Minterms */

2015-09-28T20:09:56Z

Creating Minterms

← Older revision		Revision as of 20:09, 28 September 2015
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	This means only the upper 4 bits (bits 4 to 7) of the minterm are used to select the logic operation. The lower bits (0 to 3) will always be zero because channel A is always non-zero or inside the rectangle.		This means only the upper 4 bits (bits 4 to 7) of the minterm are used to select the logic operation. The lower bits (0 to 3) will always be zero because channel A is always non-zero or inside the rectangle.

	= Creating ~~Minterms~~ =		= Creating Logic Functions =

	Creating your own logic ~~function~~ is easy if you understand there are four channels (A, B, C, D) and what each channel is assigned to do.		Creating your own logic functions is easy if you understand there are four channels (A, B, C, D) and what each channel is assigned to do.

	== Select channel A ==		== Select channel A ==

Steven Solie at 20:08, 28 September 2015

2015-09-28T20:08:28Z

@@ Line 1: / Line 1: @@
 Several graphics function calls require a ''minterm'' value to be specified which defines a logic function to perform.
-Some background knowledge of the classic Amiga blitter hardware is helpful to understand how to calculate it.
+Some background knowledge of the classic Amiga blitter hardware is helpful to understand how to derive the parameter and decode what it means.
 = Classic Amiga Blitter =
@@ Line 98: / Line 98: @@
 Channel D is always the destination channel.

← Older revision		Revision as of 21:21, 28 September 2015
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	This means only the upper 4 bits (bits 4 to 7) of the minterm are used to select the logic operation. The lower bits (0 to 3) will always be zero because channel A is always non-zero or inside the rectangle.		This means only the upper 4 bits (bits 4 to 7) of the minterm are used to select the logic operation. The lower bits (0 to 3) will always be zero because channel A is always non-zero or inside the rectangle.

	= Creating Graphics Logic Functions =		== Creating Graphics Logic Functions ==

	Creating your own graphics logic functions is easier if you understand there are four channels (A, B, C, D) and what each channel is assigned to do.		Creating your own graphics logic functions is easier if you understand there are four channels (A, B, C, D) and what each channel is assigned to do.
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	Derive the minterms required to implement the selected logic function using whatever method is most convenient.		Derive the minterms required to implement the selected logic function using whatever method is most convenient.

	== Copy Source to Destination ==		=== Copy Source to Destination ===

	To perform a simple copy from source rectangle to destination the logic function is:		To perform a simple copy from source rectangle to destination the logic function is:
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	D = B		D = B

	== Copy Inverted Source to Destination ==		=== Copy Inverted Source to Destination ===

	To perform a copy from inverted source rectangle to destination the logic function is:		To perform a copy from inverted source rectangle to destination the logic function is:
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	D = NB		D = NB

	== Copy Source and Blit Through Mask ==		=== Copy Source and Blit Through Mask ===

	To perform a copy from source rectangle to destination through a mask the logic function is:		To perform a copy from source rectangle to destination through a mask the logic function is:
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	D = B + C		D = B + C

	= Deriving Graphics Minterms =		== Deriving Graphics Minterms ==

	With our logic function determined we can then derive the minterms. Each minterm in our truth table requires both B and C channels to be present. Channel A is always non-zero as stated previously.		With our logic function determined we can then derive the minterms. Each minterm in our truth table requires both B and C channels to be present. Channel A is always non-zero as stated previously.

	== Copy Source to Destination ==		=== Copy Source to Destination ===

	As determined above, the logic function is:		As determined above, the logic function is:
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	0xC0		0xC0

	== Copy Inverted Source to Destination ==		=== Copy Inverted Source to Destination ===

	As determined above, the logic function is:		As determined above, the logic function is:
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	0x30		0x30

	== Copy Source and Blit Through Mask ==		=== Copy Source and Blit Through Mask ===

	As determined above, the logic function is:		As determined above, the logic function is: