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POEdges on polygon outlines not always correct
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  1. POEdges on polygon outlines not always correct
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    copied!<p>I'm using the algorithm below to generate quads which are then rendered to make an outline like this </p> <blockquote> <p><a href="http://img810.imageshack.us/img810/8530/uhohz.png" rel="nofollow noreferrer">http://img810.imageshack.us/img810/8530/uhohz.png</a></p> </blockquote> <p>The problem as seen on the image is that sometimes the lines are too thin when they should always be the same width. My algorithm finds the <code>4</code> vertices for the first one then the top <code>2</code> vertices of the next ones are the bottom <code>2</code> of the previous. This creates connected lines, but it seems to not always work. How could I fix this?</p> <p>This is my algorithm:</p> <pre><code> void OGLENGINEFUNCTIONS::GenerateLinePoly(const std::vector&lt;std::vector&lt;GLdouble&gt;&gt; &amp;input, std::vector&lt;GLfloat&gt; &amp;output, int width) { output.clear(); if(input.size() &lt; 2) { return; } int temp; float dirlen; float perplen; POINTFLOAT start; POINTFLOAT end; POINTFLOAT dir; POINTFLOAT ndir; POINTFLOAT perp; POINTFLOAT nperp; POINTFLOAT perpoffset; POINTFLOAT diroffset; POINTFLOAT p0, p1, p2, p3; for(unsigned int i = 0; i &lt; input.size() - 1; ++i) { start.x = static_cast&lt;float&gt;(input[i][0]); start.y = static_cast&lt;float&gt;(input[i][1]); end.x = static_cast&lt;float&gt;(input[i + 1][0]); end.y = static_cast&lt;float&gt;(input[i + 1][1]); dir.x = end.x - start.x; dir.y = end.y - start.y; dirlen = sqrt((dir.x * dir.x) + (dir.y * dir.y)); ndir.x = static_cast&lt;float&gt;(dir.x * 1.0 / dirlen); ndir.y = static_cast&lt;float&gt;(dir.y * 1.0 / dirlen); perp.x = dir.y; perp.y = -dir.x; perplen = sqrt((perp.x * perp.x) + (perp.y * perp.y)); nperp.x = static_cast&lt;float&gt;(perp.x * 1.0 / perplen); nperp.y = static_cast&lt;float&gt;(perp.y * 1.0 / perplen); perpoffset.x = static_cast&lt;float&gt;(nperp.x * width * 0.5); perpoffset.y = static_cast&lt;float&gt;(nperp.y * width * 0.5); diroffset.x = static_cast&lt;float&gt;(ndir.x * 0 * 0.5); diroffset.y = static_cast&lt;float&gt;(ndir.y * 0 * 0.5); // p0 = start + perpoffset - diroffset // p1 = start - perpoffset - diroffset // p2 = end + perpoffset + diroffset // p3 = end - perpoffset + diroffset p0.x = start.x + perpoffset.x - diroffset.x; p0.y = start.y + perpoffset.y - diroffset.y; p1.x = start.x - perpoffset.x - diroffset.x; p1.y = start.y - perpoffset.y - diroffset.y; if(i &gt; 0) { temp = (8 * (i - 1)); p2.x = output[temp + 2]; p2.y = output[temp + 3]; p3.x = output[temp + 4]; p3.y = output[temp + 5]; } else { p2.x = end.x + perpoffset.x + diroffset.x; p2.y = end.y + perpoffset.y + diroffset.y; p3.x = end.x - perpoffset.x + diroffset.x; p3.y = end.y - perpoffset.y + diroffset.y; } output.push_back(p2.x); output.push_back(p2.y); output.push_back(p0.x); output.push_back(p0.y); output.push_back(p1.x); output.push_back(p1.y); output.push_back(p3.x); output.push_back(p3.y); } } </code></pre> <hr> <p><strong>Edit:</strong></p> <pre><code> POINTFLOAT multiply(const POINTFLOAT &amp;a, float b) { POINTFLOAT result; result.x = a.x * b; result.y = a.y * b; return result; } POINTFLOAT normalize(const POINTFLOAT &amp;a) { return multiply(a, 1.0f / sqrt(a.x * a.x + a.y * a.y)); } POINTFLOAT slerp2d( const POINTFLOAT v0, const POINTFLOAT v1, float t ) { float dot = (v0.x * v1.x + v1.y * v1.y); if( dot &lt; -1.0f ) dot = -1.0f; if( dot &gt; 1.0f ) dot = 1.0f; float theta_0 = acos( dot ); float theta = theta_0 * t; POINTFLOAT v2; v2.x = -v0.y; v2.y = v0.x; POINTFLOAT result; result.x = v0.x * cos(theta) + v2.x * sin(theta); result.y = v0.y * cos(theta) + v2.y * sin(theta); return result; } void OGLENGINEFUNCTIONS::GenerateLinePoly(const std::vector&lt;std::vector&lt;GLdouble&gt; &gt; &amp;input, std::vector&lt;GLfloat&gt; &amp;output, int width) { output.clear(); if(input.size() &lt; 2) { return; } float w = width / 2.0f; //glBegin(GL_TRIANGLES); for( size_t i = 0; i &lt; input.size()-1; ++i ) { POINTFLOAT cur; cur.x = input[i][0]; cur.y = input[i][1]; POINTFLOAT nxt; nxt.x = input[i+1][0]; nxt.y = input[i+1][1]; POINTFLOAT b; b.x = nxt.x - cur.x; b.y = nxt.y - cur.y; b = normalize(b); POINTFLOAT b_perp; b_perp.x = -b.y; b_perp.y = b.x; POINTFLOAT p0; POINTFLOAT p1; POINTFLOAT p2; POINTFLOAT p3; p0.x = cur.x + b_perp.x * w; p0.y = cur.y + b_perp.y * w; p1.x = cur.x - b_perp.x * w; p1.y = cur.y - b_perp.y * w; p2.x = nxt.x + b_perp.x * w; p2.y = nxt.y + b_perp.y * w; p3.x = nxt.x - b_perp.x * w; p3.y = nxt.y - b_perp.y * w; output.push_back(p0.x); output.push_back(p0.y); output.push_back(p1.x); output.push_back(p1.y); output.push_back(p2.x); output.push_back(p2.y); output.push_back(p2.x); output.push_back(p2.y); output.push_back(p1.x); output.push_back(p1.y); output.push_back(p3.x); output.push_back(p3.y); // only do joins when we have a prv if( i == 0 ) continue; POINTFLOAT prv; prv.x = input[i-1][0]; prv.y = input[i-1][1]; POINTFLOAT a; a.x = prv.x - cur.x; a.y = prv.y - cur.y; a = normalize(a); POINTFLOAT a_perp; a_perp.x = a.y; a_perp.y = -a.x; float det = a.x * b.y - b.x * a.y; if( det &gt; 0 ) { a_perp.x = -a_perp.x; a_perp.y = -a_perp.y; b_perp.x = -b_perp.x; b_perp.y = -b_perp.y; } // TODO: do inner miter calculation // flip around normals and calculate round join points a_perp.x = -a_perp.x; a_perp.y = -a_perp.y; b_perp.x = -b_perp.x; b_perp.y = -b_perp.y; size_t num_pts = 4; std::vector&lt; POINTFLOAT&gt; round( 1 + num_pts + 1 ); POINTFLOAT nc; nc.x = cur.x + (a_perp.x * w); nc.y = cur.y + (a_perp.y * w); round.front() = nc; nc.x = cur.x + (b_perp.x * w); nc.y = cur.y + (b_perp.y * w); round.back() = nc; for( size_t j = 1; j &lt; num_pts+1; ++j ) { float t = (float)j / (float)(num_pts + 1); if( det &gt; 0 ) { POINTFLOAT nin; nin = slerp2d( b_perp, a_perp, 1.0f-t ); nin.x *= w; nin.y *= w; nin.x += cur.x; nin.y += cur.y; round[j] = nin; } else { POINTFLOAT nin; nin = slerp2d( a_perp, b_perp, t ); nin.x *= w; nin.y *= w; nin.x += cur.x; nin.y += cur.y; round[j] = nin; } } for( size_t j = 0; j &lt; round.size()-1; ++j ) { output.push_back(cur.x); output.push_back(cur.y); if( det &gt; 0 ) { output.push_back(round[j + 1].x); output.push_back(round[j + 1].y); output.push_back(round[j].x); output.push_back(round[j].y); } else { output.push_back(round[j].x); output.push_back(round[j].y); output.push_back(round[j + 1].x); output.push_back(round[j + 1].y); } } } } </code></pre>
 

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