/** Clips the input triangle against the convex, clockwise clipping area. If the triangle lies entirely within the clipping
* area, false is returned. The clipping area must duplicate the first vertex at the end of the vertices list. */
internal bool Clip(float x1, float y1, float x2, float y2, float x3, float y3, ExposedList <float> clippingArea, ExposedList <float> output)
{
var originalOutput = output;
var clipped = false;
// Avoid copy at the end.
ExposedList <float> input = null;
if (clippingArea.Count % 4 >= 2)
{
input = output;
output = scratch;
}
else
{
input = scratch;
}
input.Clear();
input.Add(x1);
input.Add(y1);
input.Add(x2);
input.Add(y2);
input.Add(x3);
input.Add(y3);
input.Add(x1);
input.Add(y1);
output.Clear();
float[] clippingVertices = clippingArea.Items;
int clippingVerticesLast = clippingArea.Count - 4;
for (int i = 0; ; i += 2)
{
float edgeX = clippingVertices[i], edgeY = clippingVertices[i + 1];
float edgeX2 = clippingVertices[i + 2], edgeY2 = clippingVertices[i + 3];
float deltaX = edgeX - edgeX2, deltaY = edgeY - edgeY2;
float[] inputVertices = input.Items;
int inputVerticesLength = input.Count - 2, outputStart = output.Count;
for (int ii = 0; ii < inputVerticesLength; ii += 2)
{
float inputX = inputVertices[ii], inputY = inputVertices[ii + 1];
float inputX2 = inputVertices[ii + 2], inputY2 = inputVertices[ii + 3];
bool side2 = deltaX * (inputY2 - edgeY2) - deltaY * (inputX2 - edgeX2) > 0;
if (deltaX * (inputY - edgeY2) - deltaY * (inputX - edgeX2) > 0)
{
if (side2) // v1 inside, v2 inside
{
output.Add(inputX2);
output.Add(inputY2);
continue;
}
// v1 inside, v2 outside
float c0 = inputY2 - inputY, c2 = inputX2 - inputX;
float ua = (c2 * (edgeY - inputY) - c0 * (edgeX - inputX)) / (c0 * (edgeX2 - edgeX) - c2 * (edgeY2 - edgeY));
output.Add(edgeX + (edgeX2 - edgeX) * ua);
output.Add(edgeY + (edgeY2 - edgeY) * ua);
}
else if (side2) // v1 outside, v2 inside
{
float c0 = inputY2 - inputY, c2 = inputX2 - inputX;
float ua = (c2 * (edgeY - inputY) - c0 * (edgeX - inputX)) / (c0 * (edgeX2 - edgeX) - c2 * (edgeY2 - edgeY));
output.Add(edgeX + (edgeX2 - edgeX) * ua);
output.Add(edgeY + (edgeY2 - edgeY) * ua);
output.Add(inputX2);
output.Add(inputY2);
}
clipped = true;
}
if (outputStart == output.Count) // All edges outside.
{
originalOutput.Clear();
return(true);
}
output.Add(output.Items[0]);
output.Add(output.Items[1]);
if (i == clippingVerticesLast)
{
break;
}
var temp = output;
output = input;
output.Clear();
input = temp;
}
if (originalOutput != output)
{
originalOutput.Clear();
for (int i = 0, n = output.Count - 2; i < n; i++)
{
originalOutput.Add(output.Items[i]);
}
}
else
{
originalOutput.Resize(originalOutput.Count - 2);
}
return(clipped);
}
public void ClipTriangles(float[] vertices, int verticesLength, int[] triangles, int trianglesLength, float[] uvs)
{
ExposedList <float> clipOutput = this.clipOutput, clippedVertices = this.clippedVertices;
var clippedTriangles = this.clippedTriangles;
var polygons = clippingPolygons.Items;
int polygonsCount = clippingPolygons.Count;
int index = 0;
clippedVertices.Clear();
clippedUVs.Clear();
clippedTriangles.Clear();
//outer:
for (int i = 0; i < trianglesLength; i += 3)
{
int vertexOffset = triangles[i] << 1;
float x1 = vertices[vertexOffset], y1 = vertices[vertexOffset + 1];
float u1 = uvs[vertexOffset], v1 = uvs[vertexOffset + 1];
vertexOffset = triangles[i + 1] << 1;
float x2 = vertices[vertexOffset], y2 = vertices[vertexOffset + 1];
float u2 = uvs[vertexOffset], v2 = uvs[vertexOffset + 1];
vertexOffset = triangles[i + 2] << 1;
float x3 = vertices[vertexOffset], y3 = vertices[vertexOffset + 1];
float u3 = uvs[vertexOffset], v3 = uvs[vertexOffset + 1];
for (int p = 0; p < polygonsCount; p++)
{
int s = clippedVertices.Count;
if (Clip(x1, y1, x2, y2, x3, y3, polygons[p], clipOutput))
{
int clipOutputLength = clipOutput.Count;
if (clipOutputLength == 0)
{
continue;
}
float d0 = y2 - y3, d1 = x3 - x2, d2 = x1 - x3, d4 = y3 - y1;
float d = 1 / (d0 * d2 + d1 * (y1 - y3));
int clipOutputCount = clipOutputLength >> 1;
float[] clipOutputItems = clipOutput.Items;
float[] clippedVerticesItems = clippedVertices.Resize(s + clipOutputCount * 2).Items;
float[] clippedUVsItems = clippedUVs.Resize(s + clipOutputCount * 2).Items;
for (int ii = 0; ii < clipOutputLength; ii += 2)
{
float x = clipOutputItems[ii], y = clipOutputItems[ii + 1];
clippedVerticesItems[s] = x;
clippedVerticesItems[s + 1] = y;
float c0 = x - x3, c1 = y - y3;
float a = (d0 * c0 + d1 * c1) * d;
float b = (d4 * c0 + d2 * c1) * d;
float c = 1 - a - b;
clippedUVsItems[s] = u1 * a + u2 * b + u3 * c;
clippedUVsItems[s + 1] = v1 * a + v2 * b + v3 * c;
s += 2;
}
s = clippedTriangles.Count;
int[] clippedTrianglesItems = clippedTriangles.Resize(s + 3 * (clipOutputCount - 2)).Items;
clipOutputCount--;
for (int ii = 1; ii < clipOutputCount; ii++)
{
clippedTrianglesItems[s] = index;
clippedTrianglesItems[s + 1] = index + ii;
clippedTrianglesItems[s + 2] = index + ii + 1;
s += 3;
}
index += clipOutputCount + 1;
}
else
{
float[] clippedVerticesItems = clippedVertices.Resize(s + 3 * 2).Items;
float[] clippedUVsItems = clippedUVs.Resize(s + 3 * 2).Items;
clippedVerticesItems[s] = x1;
clippedVerticesItems[s + 1] = y1;
clippedVerticesItems[s + 2] = x2;
clippedVerticesItems[s + 3] = y2;
clippedVerticesItems[s + 4] = x3;
clippedVerticesItems[s + 5] = y3;
clippedUVsItems[s] = u1;
clippedUVsItems[s + 1] = v1;
clippedUVsItems[s + 2] = u2;
clippedUVsItems[s + 3] = v2;
clippedUVsItems[s + 4] = u3;
clippedUVsItems[s + 5] = v3;
s = clippedTriangles.Count;
int[] clippedTrianglesItems = clippedTriangles.Resize(s + 3).Items;
clippedTrianglesItems[s] = index;
clippedTrianglesItems[s + 1] = index + 1;
clippedTrianglesItems[s + 2] = index + 2;
index += 3;
break; //continue outer;
}
}
}
}
