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When we allocate a graphene_point_t on the stack, there's no guarantee that it will be aligned at an 8-byte boundary, which is an assumption made by gsk_pathop_encode() (which wants to use the lowest 3 bits to encode the operation). In the places where it matters, force the points on the stack and embedded in structs to be nicely aligned. By using a distinct type for this (a union with a suitable size and alignment), we ensure that the compiler will warn or error whenever we can't prove that a particular point is, in fact, suitably aligned. We can go from a `GskAlignedPoint *` to a `graphene_point_t *` (which is always valid, because the `GskAlignedPoint` is aligned) via &aligned_points[0].pt, but we cannot go back the other way (which is not always valid, because the `graphene_point_t` is not necessarily aligned nicely) without a cast. In practice, it seems that a graphene_point_t on x86_64 *is* usually placed at an 8-byte boundary, but this is not the case on 32-bit architectures or on s390x. In many cases we can avoid needing an explicit reference to the more complicated type by making use of a transparent union. There's already at least one transparent union in GSK's public API, so it's presumably portable enough to match GTK's requirements. Increasing the alignment of GskAlignedPoint also requires adjusting how a GskStandardContour is allocated and initialized. This data structure allocates extra memory to hold an array of GskAlignedPoint outside the bounds of the struct itself, and that array now needs to be aligned suitably. Previously the array started with at next byte after the flexible array of gskpathop, but the alignment of a gskpathop is only 4 bytes on 32-bit architectures, so depending on the number of gskpathop in the trailing flexible array, that pointer might be an unsuitable location to allocate a GskAlignedPoint. Resolves: https://gitlab.gnome.org/GNOME/gtk/-/issues/6395 Signed-off-by: Simon McVittie <smcv@debian.org>
205 lines
9.7 KiB
C
205 lines
9.7 KiB
C
/*
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* Copyright © 2020 Benjamin Otte
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library. If not, see <http://www.gnu.org/licenses/>.
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*
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* Authors: Benjamin Otte <otte@gnome.org>
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*/
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#pragma once
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#include "gskpathopprivate.h"
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#include "gskpath.h"
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#include "gskboundingboxprivate.h"
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G_BEGIN_DECLS
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typedef gpointer gskpathop;
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typedef union _GskCurve GskCurve;
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typedef struct _GskLineCurve GskLineCurve;
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typedef struct _GskQuadCurve GskQuadCurve;
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typedef struct _GskCubicCurve GskCubicCurve;
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typedef struct _GskConicCurve GskConicCurve;
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struct _GskLineCurve
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{
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GskPathOperation op;
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gboolean padding;
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union {
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graphene_point_t points[2];
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GskAlignedPoint aligned_points[2];
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};
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};
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struct _GskQuadCurve
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{
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GskPathOperation op;
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gboolean has_coefficients;
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union {
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graphene_point_t points[3];
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GskAlignedPoint aligned_points[3];
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};
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graphene_point_t coeffs[3];
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};
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struct _GskCubicCurve
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{
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GskPathOperation op;
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gboolean has_coefficients;
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union {
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graphene_point_t points[4];
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GskAlignedPoint aligned_points[4];
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};
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graphene_point_t coeffs[4];
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};
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struct _GskConicCurve
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{
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GskPathOperation op;
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gboolean has_coefficients;
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/* points[0], points[1], points[3] are the control points,
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* points[2].x is the weight
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*/
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union {
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graphene_point_t points[4];
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GskAlignedPoint aligned_points[4];
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};
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graphene_point_t num[3];
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graphene_point_t denom[3];
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};
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union _GskCurve
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{
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GskPathOperation op;
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GskLineCurve line;
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GskQuadCurve quad;
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GskCubicCurve cubic;
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GskConicCurve conic;
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};
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typedef enum {
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GSK_CURVE_LINE_REASON_STRAIGHT,
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GSK_CURVE_LINE_REASON_SHORT
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} GskCurveLineReason;
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typedef gboolean (* GskCurveAddLineFunc) (const graphene_point_t *from,
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const graphene_point_t *to,
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float from_progress,
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float to_progress,
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GskCurveLineReason reason,
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gpointer user_data);
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typedef gboolean (* GskCurveAddCurveFunc) (GskPathOperation op,
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const graphene_point_t *pts,
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gsize n_pts,
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float weight,
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gpointer user_data);
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void gsk_curve_init (GskCurve *curve,
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gskpathop op);
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void gsk_curve_init_foreach (GskCurve *curve,
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GskPathOperation op,
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const graphene_point_t *pts,
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gsize n_pts,
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float weight);
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void gsk_curve_print (const GskCurve *curve,
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GString *string);
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char * gsk_curve_to_string (const GskCurve *curve);
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gskpathop gsk_curve_pathop (const GskCurve *curve);
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const graphene_point_t *gsk_curve_get_start_point (const GskCurve *curve);
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const graphene_point_t *gsk_curve_get_end_point (const GskCurve *curve);
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void gsk_curve_get_start_tangent (const GskCurve *curve,
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graphene_vec2_t *tangent);
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void gsk_curve_get_end_tangent (const GskCurve *curve,
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graphene_vec2_t *tangent);
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void gsk_curve_get_point (const GskCurve *curve,
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float progress,
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graphene_point_t *pos);
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void gsk_curve_get_tangent (const GskCurve *curve,
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float progress,
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graphene_vec2_t *tangent);
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void gsk_curve_reverse (const GskCurve *curve,
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GskCurve *reverse);
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void gsk_curve_split (const GskCurve *curve,
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float progress,
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GskCurve *start,
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GskCurve *end);
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void gsk_curve_segment (const GskCurve *curve,
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float start,
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float end,
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GskCurve *segment);
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gboolean gsk_curve_decompose (const GskCurve *curve,
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float tolerance,
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GskCurveAddLineFunc add_line_func,
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gpointer user_data);
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gboolean gsk_curve_decompose_curve (const GskCurve *curve,
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GskPathForeachFlags flags,
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float tolerance,
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GskCurveAddCurveFunc add_curve_func,
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gpointer user_data);
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#define gsk_curve_builder_to(curve, builder) gsk_path_builder_pathop_to ((builder), gsk_curve_pathop (curve))
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float gsk_curve_get_curvature (const GskCurve *curve,
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float t,
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graphene_point_t *center);
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void gsk_curve_get_bounds (const GskCurve *curve,
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GskBoundingBox *bounds);
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void gsk_curve_get_tight_bounds (const GskCurve *curve,
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GskBoundingBox *bounds);
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void gsk_curve_get_derivative_at (const GskCurve *curve,
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float t,
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graphene_point_t *value);
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int gsk_curve_get_crossing (const GskCurve *curve,
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const graphene_point_t *point);
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gboolean gsk_curve_get_closest_point (const GskCurve *curve,
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const graphene_point_t *point,
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float threshold,
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float *out_dist,
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float *out_t);
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float gsk_curve_get_length (const GskCurve *curve);
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float gsk_curve_get_length_to (const GskCurve *curve,
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float t);
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float gsk_curve_at_length (const GskCurve *curve,
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float distance,
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float epsilon);
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int gsk_curve_get_curvature_points (const GskCurve *curve,
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float t[3]);
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int gsk_curve_get_cusps (const GskCurve *curve,
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float t[2]);
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G_END_DECLS
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