libpicasso/Manual.md

picasso Manual

Basic concepts

Comments are introduced by the semicolon character. E.g.

; This is a comment
.fvec myFloat ; They can also appear in the same line

Identifiers follow the same rules as C identifiers.

Labels consist of an identifier plus a colon. E.g.

myLabel:
	mov r0, r1

Procedures are delimited using the .proc and .end directives. E.g.

.proc normalize3
	dp4 r15, r8, r8
	rsq r15, r15
	mul r8, r15, r8
.end

Instructions consist of an opcode name and a comma-delimited list of arguments.

Directives are special statements that start with a period and control certain aspects of picasso's code emission; such as defining procedures, uniforms, constants and more.

PICA200 registers are often used as arguments to instructions. There exist the following registers:

• o0 through o7: Output registers (usable as a destination operand).
• v0 through v7: Input registers (usable as a source operand).
• r0 through r15: Scratch registers (usable as both destination and source operands).
• c0 through c95: Floating-point vector uniforms (usable as a special type of source operand called SRC1).
• i0 through i3: Integer vector uniforms (special purpose).
• b0 through b15: Boolean uniforms (special purpose).

All registers contain floating point vectors (it is currently unknown whether they are 24-bit or 32-bit); except for integer vector uniforms (containing 8-bit integers) and boolean uniforms. Vectors have 4 components: x, y, z and w. Uniforms are special registers that are writable by the CPU; thus they are used to pass configuration parameters to the shader such as transformation matrices. Sometimes they are preloaded with constant values that may be used in the logic of the shader.

In most situations, vectors may be swizzled, that is; their components may be rearranged. Register arguments support specifying a swizzling mask: r0.wwxy. The swizzling mask usually has 4 components (but not more), if it has less the last component is repeated to fill the mask. The default mask applied to registers is xyzw; that is, identity (no effect).

Output parameters have an output mask instead of a swizzling mask. This allows the shader to write to some components of a register without affecting the others. In picasso, the output mask is parsed exactly the same way as the swizzling mask, enabling write access for the components that are used in it. By default it is also xyzw; that is, writing to all components.

Registers may also be assigned additional names in order to make the code more legible. These additional names are called aliases. Aliases may also contain a swizzling mask; if a swizzling mask is applied to an alias afterwards the masks are combined. For example, provided that someAlias is an alias for c0.wyxz, someAlias.xxww would be equivalent to c0.wwzz. Aliases may be created by several directives which reserve certain kinds of registers.

For convenience, registers may be addressed using an offset from a known register. This is called indexing. For example, c8[4] is equivalent to c12; and r4[-2] is equivalent to r2. Indexing is useful for addressing arrays of registers (such as matrices).

Some source operands of instructions (called SRC1) support relative addressing. This means that it is possible to use one of the three built-in indexing registers (a0, a1 and a2 aka lcnt) to address a register, e.g. someArray[lcnt]. Adding an offset is also supported, e.g. someArray[lcnt+2]. This is useful in FOR loops.

Normal floating-point vector registers may also be negated by prepending a minus sign before it, e.g. -r2 or -someArray[lcnt+2].

Command Line Usage

Usage: picasso [options] files...
Options:
  -o, --out=<file>        Specifies the name of the SHBIN file to generate
  -h, --header=<file>     Specifies the name of the header file to generate

DVLEs are generated in the same order as the files in the command line.

Linking Model

picasso takes one or more source code files, and assembles them into a single .shbin file. A DVLE object is generated for each source code file, unless the .nodvle directive is used (see below). Procedures are shared amongst all source code files, and they may be defined and called wherever. Uniform space is also shared, that is, if two source code files declare the same uniform, they are assigned the same location. Constants however are not shared, and the same space is reused for the constants of each DVLE. Outputs and aliases are necessarily not shared either.

The entry point of a DVLE may be set with the .entry directive. If this directive is not used, main is assumed as the entrypoint.

A DVLE is marked by default as a vertex shader, unless setemit or .gsh are used (in the case of which a geometry shader is assumed).

Uniforms that start with the underscore (_) character are not exposed in the DVLE table of uniforms. This allows for creating private uniforms that can be internally used to configure the behaviour of shared procedures.

Supported Directives

.proc

.proc procName

Introduces a procedure called procName. The procedure is terminated with .end.

.else

.else

Introduces the ELSE section of an IF statement.

.end

.end

Terminates a procedure, an IF statement or a FOR statement.

.alias

.alias aliasName register

Creates a new alias for register called aliasName. The specified register may also have a swizzling mask.

.fvec

.fvec unifName1, unifName2[size], unifName3, ...

Allocates new floating-point vector uniforms (or arrays of uniforms) and creates aliases for them that point to the allocated registers. Example:

.fvec scaler
.fvec projMatrix[4], modelViewMatrix[4]

.ivec

.ivec unifName1, unifName2[size], unifName3, ...

Allocates new integer vector uniforms (or arrays of uniforms) and creates aliases for them that point to the allocated registers.

.bool

.bool unifName1, unifName2[size], unifName3, ...

Allocates new boolean uniforms (or arrays of uniforms) and creates aliases for them that point to the allocated registers. Example:

.bool useLight[4]
.bool useRawVertexColor

.constf

.constf constName(x, y, z, w)

Reserves a new floating-point vector uniform to be preloaded with the specified constant; creates an alias for it that points to the allocated register. Example:

.constf floatConsts(0.0, 1.0, -1.0, 3.14159)

.consti

.consti constName(x, y, z, w)

Reserves a new integer vector uniform to be preloaded with the specified constant; creates an alias for it that points to the allocated register. Example:

.constf loopParams(16, 0, 1, 0)

.out

.out outName propName

Allocates a new output register, wires it to a certain output property and creates an alias for it that points to the allocated register. The following property names are supported:

• position (or pos): Represents the position of the outputted vertex.
• normalquat (or nquat): Under investigation.
• color (or clr): Represents the color of the outputted vertex. Its format is (R, G, B, xx) where R,G,B are values ranging from 0.0 to 1.0. The W component isn't used.
• texcoord0 (or tcoord0): Represents the texture coordinate that is fed to the Texture Unit 0. The Z and W components are not used.
• texcoord0w (or tcoord0w): Under investigation.
• texcoord1 (or tcoord1): As texcoord0, but for the Texture Unit 1.
• texcoord2 (or tcoord2): As texcoord0, but for the Texture Unit 2.
• 7: Under investigation.
• view: Under investigation.

The properties also accept an output mask, e.g. texcoord0.xy.

Example:

.out outPos position
.out outClr color
.out outTex texcoord0

.entry

.entry procedureName

Specifies the name of the procedure to use as the entrypoint of the current DVLE. If this directive is not used, main is assumed.

.nodvle

.nodvle

This directive tells picasso not to generate a DVLE for the source code file that is being processed. This allows for writing files that contain shared procedures to be used by other files.

.gsh

.gsh

This directive explicitly flags the current DVLE as a geometry shader.

.setf

.setf register(x, y, z, w)

Similar to .constf, this directive adds a DVLE constant entry for the specified floating-point vector uniform register to be loaded with the specified value. This is useful in order to instantiate a generalized shared procedure with the specified parameters.

.seti

.seti register(x, y, z, w)

Similar to .consti, this directive adds a DVLE constant entry for the specified integer vector uniform register to be loaded with the specified value. This is useful in order to instantiate a generalized shared procedure with the specified parameters.

.setb

.setb register value

This directive adds a DVLE constant entry for the specified boolean uniform register to be loaded with the specified value (which may be true, false, on, off, 1 or 0). This is useful in order to control the flow of a generalized shared procedure.

Supported Instructions

See Shader Instruction Set for more details.

Syntax	Description
nop	No operation.
end	Signals the end of the program.
emit	(Geoshader-only) Emits a vertex configured by a prior setemit.
setemit vtxId, emitFlags	(Geoshader-only) Configures a vertex for emission. The emitFlags parameter can be omitted.
add rDest, rSrc1, rSrc2
dp3 rDest, rSrc1, rSrc2
dp4 rDest, rSrc1, rSrc2
dph rDest, rSrc1, rSrc2
mul rDest, rSrc1, rSrc2
sge rDest, rSrc1, rSrc2
slt rDest, rSrc1, rSrc2
max rDest, rSrc1, rSrc2
min rDest, rSrc1, rSrc2
ex2 rDest, rSrc1
lg2 rDest, rSrc1
ex2 rDest, rSrc1
flr rDest, rSrc1
rcp rDest, rSrc1
rsq rDest, rSrc1
mov rDest, rSrc1
mova rSrc1
cmp rSrc1, opx, opy, rSrc2
call procName
for iReg
breakc condExp
callc condExp, procName
ifc condExp
jmpc condExp, labelName
callu bReg, procName
ifu bReg
jmpu bReg, labelName
mad rDest, rSrc1, rSrc2, rSrc3

Description of operands

• rDest: Represents a destination operand (register).
• rSrc1/rSrc2/rSrc3: Represents a source operand (register). Depending on the position, some registers may be supported and some may not.
  • Narrow source operands are limited to input and scratch registers.
  • Wide source operands also support floating-point vector uniforms and relative addressing.
  • In instructions that take one source operand, it is always wide.
  • In instructions that take two source operands, the first is wide and the second is narrow.
  • dph/sge/slt have a special form where the first operand is narrow and the second is wide. This usage is detected automatically by picasso.
  • mad, which takes three source operands, has two forms: the first is wide-wide-narrow, and the second is wide-narrow-wide. This is also detected automatically. Additionally, relative addressing is not supported.
• iReg: Represents an integer vector uniform source operand.
• bReg: Represents a boolean uniform source operand.
• procName: Represents the name of a procedure.
• labelName: Represents the name of a label.
• opx and opy: They represent a conditional operator that is applied to the source registers and whose result is stored in the appropriate flag (cmp.x and cmp.y respectively). Supported values include:
  • eq: Equal
  • ne: Not equal
  • lt: Less than
  • le: Less or equal than
  • gt: Greater than
  • ge: Greater or equal than
  • 6 and 7: currently unknown, supposedly the result they yield is always true.
• condExp: Represents a conditional expression, which uses the conditional flags cmp.x and cmp.y set by the CMP instruction. These flags may be negated using the ! symbol, e.g. !cmp.x. The conditional expression can take any of the following forms:
  • flag1: It tests a single flag.
  • flag1 && flag2: It performs AND between the two flags. Optionally, a single & may be specified.
  • flag1 || flag2: It performs OR between the two flags. Optionally, a single | may be specified.
• vtxId: An integer ranging from 0 to 3 specifying the vertex ID used in geoshader vertex emission.
• emitFlags: A space delimited combination of the following words:
  • primitive (or prim): Specifies that after emitting the vertex, a primitive should also be emitted.
  • inv (or invert): Specifies that the order of the vertices in the emitted primitive is inverted.