/** 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; } } } }