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Fix line drawing artefact with nearly parallel segments.

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This commit is contained in:
vrld
2013-08-08 21:37:11 +02:00
parent 9d0c01be4a
commit 8b53bc385e
1 changed files with 12 additions and 15 deletions
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src/modules/graphics/opengl/Polyline.cpp
+12 -15
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@@ -18,7 +18,7 @@
* 3. This notice may not be removed or altered from any source distribution.
**/
#include <iostream>
#include <algorithm>
// LOVE
#include "Polyline.h"
@@ -26,8 +26,8 @@
// OpenGL
#include "OpenGL.h"
// treat adjacent segments with angles between their normals <7 degree as straight
static const float LINES_PARALLEL_EPS = 0.15;
// treat adjacent segments with angles between their directions <5 degree as straight
static const float LINES_PARALLEL_EPS = 0.05;
namespace love
{
@@ -123,19 +123,19 @@ void NoneJoinPolyline::renderEdge(std::vector<Vector> &anchors, std::vector<Vect
* u1/u2 are the intersection points of the parallel lines to p-q and q-r,
* i.e. the point where
*
* (p + w/2 * ns) + lambda * (q - p) = (q + w/2 * nt) + mu * (r - q) (u1)
* (p - w/2 * ns) + lambda * (q - p) = (q - w/2 * nt) + mu * (r - q) (u2)
* (q + w/2 * ns) + lambda * (q - p) = (q + w/2 * nt) + mu * (r - q) (u1)
* (q - w/2 * ns) + lambda * (q - p) = (q - w/2 * nt) + mu * (r - q) (u2)
*
* with nt,nt being the normals on the segments s = p-q and t = q-r,
*
* ns = perp(s) / |s|
* nt = perp(t) / |s|.
* nt = perp(t) / |t|.
*
* Using the linear equation system (similar for u2)
*
* p + w/2 * ns + lambda * s - (q + w/2 * nt + mu * t) = 0 (u1)
* <=> (p-q) + lambda * s - mu * t = (nt - ns) * w/2
* <=> (lambda - 1) * s - mu * t = (nt - ns) * w/2
* q + w/2 * ns + lambda * s - (q + w/2 * nt + mu * t) = 0 (u1)
* <=> q-q + lambda * s - mu * t = (nt - ns) * w/2
* <=> lambda * s - mu * t = (nt - ns) * w/2
*
* the intersection points can be efficiently calculated using Cramer's rule.
*/
@@ -151,7 +151,7 @@ void MiterJoinPolyline::renderEdge(std::vector<Vector> &anchors, std::vector<Vec
anchors.push_back(q);
float det = s ^ t;
if (fabs(det) / (len_s * len_t) < LINES_PARALLEL_EPS)
if (fabs(det) / (len_s * len_t) < LINES_PARALLEL_EPS && s * t > 0)
{
// lines parallel, compute as u1 = q + ns * w/2, u2 = q - ns * w/2
normals.push_back(ns);
@@ -196,7 +196,7 @@ void BevelJoinPolyline::renderEdge(std::vector<Vector> &anchors, std::vector<Vec
float len_t = t.getLength();
float det = s ^ t;
if (fabs(det) / (len_s * len_t) < LINES_PARALLEL_EPS)
if (fabs(det) / (len_s * len_t) < LINES_PARALLEL_EPS && s * t > 0)
{
// lines parallel, compute as u1 = q + ns * w/2, u2 = q - ns * w/2
Vector n = t.getNormal(hw / len_t);
@@ -338,8 +338,6 @@ void Polyline::draw()
if (overdraw)
{
// prepare colors:
// even indices in overdraw* point to inner vertices => alpha = current-alpha,
// odd indices point to outer vertices => alpha = 0.
Color c = gl.getColor();
Color *colors = new Color[overdraw_vertex_count];
fill_color_array(colors, c);
@@ -374,8 +372,7 @@ void NoneJoinPolyline::fill_color_array(Color *colors, const Color &c)
{
colors[i] = c;
// if (i % 4 == 1 || i % 4 == 2) colors[i].a = 0
size_t k = i % 4;
colors[i].a *= GLubyte(k != 1 && k != 2);
colors[i].a *= GLubyte((i+1) % 4 < 2);
}
}