From a2ec68f960ddd853d01226c50ed35f76b05d64ba Mon Sep 17 00:00:00 2001
From: Luke Benstead <kazade@gmail.com>
Date: Tue, 6 Apr 2021 13:09:40 +0100
Subject: [PATCH] Start implementing triangle rasterizer

---
 GL/platforms/software/edge_equation.c      | 20 ++++++++++++++++++++
 GL/platforms/software/edge_equation.h      | 17 +++++++++++++++++
 GL/platforms/software/parameter_equation.c | 16 ++++++++++++++++
 GL/platforms/software/parameter_equation.h | 16 ++++++++++++++++
 4 files changed, 69 insertions(+)
 create mode 100644 GL/platforms/software/edge_equation.c
 create mode 100644 GL/platforms/software/edge_equation.h
 create mode 100644 GL/platforms/software/parameter_equation.c
 create mode 100644 GL/platforms/software/parameter_equation.h

diff --git a/GL/platforms/software/edge_equation.c b/GL/platforms/software/edge_equation.c
new file mode 100644
index 0000000..6a6c7cb
--- /dev/null
+++ b/GL/platforms/software/edge_equation.c
@@ -0,0 +1,20 @@
+#include "edge_equation.h"
+
+void EdgeEquationInit(EdgeEquation* edge, const float* v0, const float* v1) {
+    edge->a = v0[1] - v1[1];
+    edge->b = v1[0] - v0[0];
+    edge->c = -(edge->a * (v0[0] + v1[0]) + edge->b * (v0[1] + v1[1])) / 2;
+    edge->tie = edge->a != 0 ? edge->a > 0 : edge->b > 0;
+}
+
+float EdgeEquationEvaluate(const EdgeEquation* edge, float x, float y) {
+    return edge->a * x + edge->b * y + edge->c;
+}
+
+bool EdgeEquationTestValue(const EdgeEquation* edge, float value) {
+    return (value >= 0 || (value == 0 && edge->tie));
+}
+
+bool EdgeEquationTestPoint(const EdgeEquation* edge, float x, float y) {
+    return EdgeEquationTestValue(edge, EdgeEquationEvaluate(edge, x, y));
+}
diff --git a/GL/platforms/software/edge_equation.h b/GL/platforms/software/edge_equation.h
new file mode 100644
index 0000000..2bd1bde
--- /dev/null
+++ b/GL/platforms/software/edge_equation.h
@@ -0,0 +1,17 @@
+#pragma once
+
+#include <stdint.h>
+#include <stdbool.h>
+
+typedef struct EdgeEquation {
+    float a;
+    float b;
+    float c;
+    bool tie;
+} EdgeEquation;
+
+void EdgeEquationInit(EdgeEquation* edge, const float* v0, const float* v1);
+float EdgeEquationEvaluate(const EdgeEquation* edge, float x, float y);
+bool EdgeEquationTestValue(const EdgeEquation* edge, float value);
+bool EdgeEquationTestPoint(const EdgeEquation* edge, float x, float y);
+
diff --git a/GL/platforms/software/parameter_equation.c b/GL/platforms/software/parameter_equation.c
new file mode 100644
index 0000000..cf46299
--- /dev/null
+++ b/GL/platforms/software/parameter_equation.c
@@ -0,0 +1,16 @@
+#include "parameter_equation.h"
+#include "edge_equation.h"
+
+void ParameterEquationInit(ParameterEquation* equation, float p0, float p1, float p2, const EdgeEquation* e0, const EdgeEquation* e1, const EdgeEquation* e2, float area) {
+
+    float factor = 1.0f / (2.0f * area);
+
+    equation->a = factor * (p0 * e0->a + p1 * e1->a + p2 * e2->a);
+    equation->b = factor * (p0 * e0->b + p1 * e1->b + p2 * e2->b);
+    equation->c = factor * (p0 * e0->c + p1 * e1->c + p2 * e2->c);
+}
+
+
+float ParameterEquationEvaluate(const ParameterEquation* equation, float x, float y) {
+    return equation->a * x + equation->b * y + equation->c;
+}
diff --git a/GL/platforms/software/parameter_equation.h b/GL/platforms/software/parameter_equation.h
new file mode 100644
index 0000000..7aea832
--- /dev/null
+++ b/GL/platforms/software/parameter_equation.h
@@ -0,0 +1,16 @@
+#pragma once
+
+typedef struct ParameterEquation {
+    float a;
+    float b;
+    float c;
+} ParameterEquation;
+
+struct EdgeEquation;
+
+void ParameterEquationInit(
+    ParameterEquation* equation,
+    float p0, float p1, float p2,
+    const EdgeEquation* e0, const EdgeEquation* e1, const EdgeEquation* e2, float area);
+
+float ParameterEquationEvaluate(const ParameterEquation* equation, float x, float y);