Why does my triangle rasterization miss some pixels along one edge?

I am having an issue rasterizing a triangle. The goal is to calculate barycentric coordinates and make the triangle based off those coordinates. I am having an issue with having weird jaggy missing pixels on one of my edges. The code is pretty messy currently but here is what I've got:

#include <iostream> #include <string> #include <vector> #include <memory> #include <algorithm> #include "Image.h" // This allows you to skip the `std::` in front of C++ standard library // functions. You can also say `using std::cout` to be more selective. // You should never do this in a header file. using namespace std; struct boundingBox{ int xmin; int xmax; int ymin; int ymax; } box; struct Triangle{ int xCoordA; int yCoordA; int xCoordB; int yCoordB; int xCoordC; int yCoordC; } t; struct Point{ float x; float y; } P; int main(int argc, char **argv) { if(argc < 19 || argc > 19) { cout << "Usage: L02 filename width height Vertex1-x Vertex1-y Vertex1-Red Vertex-1-Green Vertex-1-Blue Vertex2-x Vertex2-y Vertex-2-Red Vertex-2-Green Vertex2-2-Blue Vertex3-x Vertex3-y Vertex-3-Red Vertex-3-Green Vertex-3-Blue" << endl; return 0; } // Output filename string filename(argv[1]); // Width of image int width = atoi(argv[2]); // Height of image int height = atoi(argv[3]); // Coordinates of vertex 1 t.xCoordA = atoi(argv[4]); t.yCoordA = atoi(argv[5]); //color of vertex 1 int red1 = atoi(argv[6]); int green1 = atoi(argv[7]); int blue1 = atoi(argv[8]); //coordinates of vertex 2 t.xCoordB = atoi(argv[9]); t.yCoordB = atoi(argv[10]); //color of vertex 2 int red2 = atoi(argv[11]); int green2 = atoi(argv[12]); int blue2 = atoi(argv[13]); //coordinates of vertex 3 t.xCoordC = atoi(argv[14]); t.yCoordC = atoi(argv[15]); //color of vertex 3 int red3 = atoi(argv[16]); int green3 = atoi(argv[17]); int blue3 = atoi(argv[18]); // Find bounding box values int xMaxTemp = max((t.xCoordA), (t.xCoordB)); box.xmax = max(xMaxTemp, (t.xCoordC)); int yMaxTemp = max((t.yCoordA), (t.yCoordB)); box.ymax = max(yMaxTemp, (t.yCoordC)); int xMinTemp = min((t.xCoordA), (t.xCoordB)); box.xmin = min(xMinTemp, (t.xCoordC)); int yMinTemp = min((t.yCoordA), (t.yCoordB)); box.ymin = min(yMinTemp, (t.yCoordC)); // Create the image. We're using a `shared_ptr`, a C++11 feature. auto image = make_shared<Image>(width, height); for (int i = box.xmin; i <= box.xmax; i++) { for (int j = box.ymin; j <= box.ymax; j++) { P.x = static_cast<float>(i); P.y = static_cast<float>(j); float denAlpha = ((t.yCoordB - t.yCoordC) * t.xCoordA + (t.xCoordC - t.xCoordB) * t.yCoordA + (t.xCoordB * t.yCoordC) - (t.xCoordC * t.yCoordB)); float denBeta = ((t.yCoordC - t.yCoordA) * t.xCoordB + (t.xCoordA - t.xCoordC) * t.yCoordB + (t.xCoordC * t.yCoordA) - (t.xCoordA * t.yCoordC)); float numAlpha = ((t.yCoordB - t.yCoordC) * P.x + (t.xCoordC - t.xCoordB) * P.y + (t.xCoordB * t.yCoordC) - (t.xCoordC * t.yCoordB)); float numBeta = ((t.yCoordC - t.yCoordA) * P.x + (t.xCoordA - t.xCoordC) * P.y + (t.xCoordC * t.yCoordA) - (t.xCoordA * t.yCoordC)); float alpha = numAlpha / denAlpha; float beta = numBeta / denBeta; float gamma = 1.0 - alpha - beta; if (alpha >= 0.0 && beta >= 0.0 && gamma >= 0.0) { //Then we are in triangle int myRed = (red1 * alpha) + (red2 * beta) + (red3 * gamma); int myGreen = (green1 * alpha) + (green2 * beta) + (green3 * gamma); int myBlue = (blue1 * alpha) + (blue2 * beta) + (blue3 * gamma); image->setPixel(P.x, P.y, myRed, myGreen, myBlue); } else{ //we are not in triangle image->setPixel(P.x, P.y, 0, 0, 0); } } } image->writeToFile(filename); return 0; } 

I should only need to check if the coordinates are >= 0 since I am using the bounding box to check the other side.

For some reason when I run it this is what the triangle looks like

The hypotenuse has weird jaggy/ missing pixel edges.

I have been working with my instructor for 2 whole lab sessions now, and changing the way I calculate the bary-coordinates hasn't solved anything.