| // Copyright 2020 The Fuchsia Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| // |
| // |
| // |
| |
| #include "spinel/ext/geometry/ellipse.h" |
| |
| #include "spinel/spinel_assert.h" |
| |
| // |
| // Not a constant found in <math.h> |
| // |
| |
| #ifndef SPN_M_SQRT3_2 |
| |
| #define SPN_M_SQRT3_2 0.86602540378443864676 // sqrt(3)/2 |
| |
| #endif |
| |
| // |
| // |
| // |
| |
| // clang-format off |
| #define SPN_SWEEP_COS_2 0.5f // cosf(120° / 2.0) |
| #define SPN_SWEEP_SIN_2 (float)SPN_M_SQRT3_2 // sinf(120° / 2.0) |
| #define SPN_SWEEP_K 0.5f // 2.0 * 0.5 * 0.5 |
| #define SPN_SWEEP_K_INV 2.0f // 1 / 0.5 |
| // clang-format on |
| |
| // |
| // |
| // |
| |
| #define SPN_ELLIPSE_SWEEP(x1_, y1_, x2_, y2_) \ |
| if ((err = spinel_path_builder_rat_quad_to(path_builder, /* */ \ |
| x1_, \ |
| y1_, \ |
| x2_, \ |
| y2_, \ |
| SPN_SWEEP_COS_2)) != SPN_SUCCESS) \ |
| return err; |
| |
| // |
| // Draw an ellipse with 3 rational quads |
| // |
| spinel_result_t |
| spinel_path_builder_ellipse(spinel_path_builder_t path_builder, // |
| float cx, |
| float cy, |
| float rx, |
| float ry) |
| { |
| // |
| // calculate 3 end points |
| // |
| float const px0 = cx + rx; |
| float const py0 = cy; |
| |
| float const pxE = cx - rx * SPN_SWEEP_COS_2; |
| float const py1 = cy + ry * SPN_SWEEP_SIN_2; |
| |
| // px2 = px1 |
| float const py2 = cy - ry * SPN_SWEEP_SIN_2; |
| |
| // |
| // calculate 3 control points using A. Cantóna method |
| // |
| float const qx0 = (cx * (SPN_SWEEP_K - 2.0f) + px0 + pxE) * SPN_SWEEP_K_INV; |
| float const qy0 = (cy * (SPN_SWEEP_K - 2.0f) + py0 + py1) * SPN_SWEEP_K_INV; |
| |
| float const qx1 = (cx * (SPN_SWEEP_K - 2.0f) + pxE + pxE) * SPN_SWEEP_K_INV; |
| float const qy1 = (cy * (SPN_SWEEP_K - 2.0f) + py1 + py2) * SPN_SWEEP_K_INV; |
| |
| float const qx2 = (cx * (SPN_SWEEP_K - 2.0f) + pxE + px0) * SPN_SWEEP_K_INV; |
| float const qy2 = (cy * (SPN_SWEEP_K - 2.0f) + py2 + py0) * SPN_SWEEP_K_INV; |
| |
| // |
| // emit 3 arc control cages |
| // |
| spinel_path_builder_move_to(path_builder, px0, py0); |
| |
| spinel_result_t err; |
| |
| SPN_ELLIPSE_SWEEP(qx0, qy0, pxE, py1); |
| SPN_ELLIPSE_SWEEP(qx1, qy1, pxE, py2); |
| SPN_ELLIPSE_SWEEP(qx2, qy2, px0, py0); |
| |
| return SPN_SUCCESS; |
| } |
| |
| // |
| // |
| // |
