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).
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](http://en.wikipedia.org/wiki/Swizzling_%28computer_graphics%29), 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.
`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.
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:
-`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.
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.
-`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.
-`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:
-`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.
