The theme expression parser

Themes can use a simple expression language to represent the values of things. More...

Data Structures
struct	PosExpr
	Type and value of an expression in a parsed sequence. More...
struct	_MetaDrawSpec
	A computed expression in our simple vector drawing language. More...
Typedefs
typedef struct _MetaDrawSpec	MetaDrawSpec
Enumerations
enum	PosExprType { POS_EXPR_INT, POS_EXPR_DOUBLE, POS_EXPR_OPERATOR }
	The type of a PosExpr: either integer, double, or an operation. More...
Functions
static gboolean	pos_eval_get_variable (PosToken *t, int *result, const MetaPositionExprEnv *env, GError **err)
	There is a predefined set of variables which can appear in an expression.
static gboolean	pos_eval_helper (PosToken *tokens, int n_tokens, const MetaPositionExprEnv *env, PosExpr *result, GError **err)
	Evaluates a sequence of tokens within a particular environment context, and returns the current value.
static gboolean	pos_eval (MetaDrawSpec *spec, const MetaPositionExprEnv *env, int *val_p, GError **err)
	Evaluates an expression.

---

Detailed Description

Themes can use a simple expression language to represent the values of things.

This is the parser used for that language.

---

Typedef Documentation

typedef struct _MetaDrawSpec MetaDrawSpec

---

Enumeration Type Documentation

enum PosExprType

The type of a PosExpr: either integer, double, or an operation.

Enumerator:

POS_EXPR_INT
POS_EXPR_DOUBLE
POS_EXPR_OPERATOR

Definition at line 1825 of file theme.c.

---

Function Documentation

static gboolean pos_eval	(	MetaDrawSpec *	spec,
		const MetaPositionExprEnv *	env,
		int *	val_p,
		GError **	err
	)			[static]

Evaluates an expression.

Parameters:

	spec	The expression to evaluate.
	env	The environment context to evaluate the expression in.
[out]	val_p	The integer value of the expression; if the expression is of type float, this will be rounded. If we return FALSE because the expression is invalid, this will be zero.
[out]	err	The error, if anything went wrong.

Returns:

True if we evaluated the expression successfully; false otherwise.

Bug:

Shouldn't spec be const?

Definition at line 2439 of file theme.c.

References PosExpr::d, PosExpr::double_val, FALSE, PosExpr::int_val, _MetaDrawSpec::n_tokens, pos_eval_helper(), POS_EXPR_DOUBLE, POS_EXPR_INT, POS_EXPR_OPERATOR, _MetaDrawSpec::tokens, TRUE, and PosExpr::type.

Referenced by meta_draw_spec_new(), meta_parse_position_expression(), and meta_parse_size_expression().

static gboolean pos_eval_get_variable	(	PosToken *	t,
		int *	result,
		const MetaPositionExprEnv *	env,
		GError **	err
	)			[static]

There is a predefined set of variables which can appear in an expression.

Here we take a token representing a variable, and return the current value of that variable in a particular environment. (The value is always an integer.)

There are supposedly some circumstances in which this function can be called from outside Metacity, in which case env->theme will be NULL, and therefore we can't use it to find out quark values, so we do the comparison using strcmp, which is slower.

Parameters:

	t	The token representing a variable
[out]	result	The value of that variable; not set if the token did not represent a known variable
	env	The environment within which t should be evaluated
[out]	err	set to the problem if there was a problem

Returns:

true if we found the variable asked for, false if we didn't

Bug:

shouldn't t be const?

Bug:

we should perhaps consider some sort of lookup arrangement into an array; also, the duplication of code is unlovely; perhaps using glib string hashes instead of quarks would fix both problems?

Definition at line 2156 of file theme.c.

References _, _MetaPositionExprEnv::bottom_height, PosToken::d, FALSE, _MetaRectangle::height, _MetaPositionExprEnv::icon_height, _MetaPositionExprEnv::icon_width, _MetaPositionExprEnv::left_width, META_THEME_ERROR, META_THEME_ERROR_UNKNOWN_VARIABLE, _MetaPositionExprEnv::mini_icon_height, _MetaPositionExprEnv::mini_icon_width, _MetaPositionExprEnv::object_height, _MetaPositionExprEnv::object_width, _MetaTheme::quark_bottom_height, _MetaTheme::quark_height, _MetaTheme::quark_icon_height, _MetaTheme::quark_icon_width, _MetaTheme::quark_left_width, _MetaTheme::quark_mini_icon_height, _MetaTheme::quark_mini_icon_width, _MetaTheme::quark_object_height, _MetaTheme::quark_object_width, _MetaTheme::quark_right_width, _MetaTheme::quark_title_height, _MetaTheme::quark_title_width, _MetaTheme::quark_top_height, _MetaTheme::quark_width, _MetaPositionExprEnv::rect, _MetaPositionExprEnv::right_width, _MetaPositionExprEnv::theme, _MetaPositionExprEnv::title_height, _MetaPositionExprEnv::title_width, _MetaPositionExprEnv::top_height, TRUE, and _MetaRectangle::width.

Referenced by pos_eval_helper().

static gboolean pos_eval_helper	(	PosToken *	tokens,
		int	n_tokens,
		const MetaPositionExprEnv *	env,
		PosExpr *	result,
		GError **	err
	)			[static]

Evaluates a sequence of tokens within a particular environment context, and returns the current value.

May recur if parantheses are found.

Parameters:

	tokens	A list of tokens to evaluate.
	n_tokens	How many tokens are in the list.
	env	The environment context in which to evaluate the expression.
[out]	result	The current value of the expression

Bug:

Yes, we really do reparse the expression every time it's evaluated. We should keep the parse tree around all the time and just run the new values through it.

Definition at line 2262 of file theme.c.

References _, PosToken::d, PosExpr::d, do_operations(), PosExpr::double_val, FALSE, PosExpr::int_val, MAX_EXPRS, META_THEME_ERROR, META_THEME_ERROR_BAD_PARENS, META_THEME_ERROR_FAILED, PosExpr::operator, pos_eval_get_variable(), POS_EXPR_DOUBLE, POS_EXPR_INT, POS_EXPR_OPERATOR, POS_TOKEN_CLOSE_PAREN, POS_TOKEN_DOUBLE, POS_TOKEN_INT, POS_TOKEN_OPEN_PAREN, POS_TOKEN_OPERATOR, POS_TOKEN_VARIABLE, TRUE, PosExpr::type, and PosToken::type.

Referenced by pos_eval().