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1 files changed, 64 insertions, 0 deletions

diff --git a/src/vec4ops/vec4ops.cpp b/src/vec4ops/vec4ops.cpp
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+++ b/src/vec4ops/vec4ops.cpp
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+#include <stdexcept>
+#include "vec4ops.h"
+
+// vector operations on 4d vectors,
+// reference: https://hollasch.github.io/ray4/Four-Space_Visualization_of_4D_Objects.html#chapter5
+
+glm::vec4 Vec4Ops::cross4(
+        glm::vec4 u,
+        glm::vec4 v,
+        glm::vec4 w) {
+    float a = (v[0] * w[1]) - (v[1] * w[0]);
+    float b = (v[0] * w[2]) - (v[2] * w[0]);
+    float c = (v[0] * w[3]) - (v[3] * w[0]);
+    float d = (v[1] * w[2]) - (v[2] * w[1]);
+    float e = (v[1] * w[3]) - (v[3] * w[1]);
+    float f = (v[2] * w[3]) - (v[3] * w[2]);
+
+    glm::vec4 result;
+    result[0] = (u[1] * f) - (u[2] * e) + (u[3] * d);
+    result[1] = -(u[0] * f) + (u[2] * c) - (u[3] * b);
+    result[2] = (u[0] * e) - (u[1] * c) + (u[3] * a);
+    result[3] = -(u[0] * d) + (u[1] * b) - (u[2] * a);
+
+    return result;
+}
+
+glm::vec4 Vec4Ops::dot4(
+        glm::vec4 u,
+        glm::vec4 v) {
+    return {u[0] * v[0], u[1] * v[1], u[2] * v[2], u[3] * v[3]};
+}
+
+glm::mat4 Vec4Ops::getViewMatrix4(
+        glm::vec4 fromPoint,
+        glm::vec4 toPoint,
+        glm::vec4 upVector,
+        glm::vec4 lookVector) {
+
+    // calculate e3 basis vector, the transformation col of view matrix
+    if (glm::distance(fromPoint, toPoint) < 0.0001f) {
+        throw std::runtime_error("fromPoint and toPoint are the same");
+    }
+    glm::vec4 e3 = glm::normalize(fromPoint - toPoint);
+
+    // calculate e2 basis vector, from the combinatory cross of up and over with e3
+    glm::vec4 e2 = cross4(upVector, lookVector, e3);
+    e2 = glm::normalize(e2);
+    if (glm::distance(e2, glm::vec4{0, 0, 0, 0}) < 0.0001f) {
+        throw std::runtime_error("invalid up vector");
+    }
+
+    // calculate e1 basis vector, from the cross of only the over vector
+    glm::vec4 e1 = cross4(lookVector, e3, e2);
+    e1 = glm::normalize(e1);
+    if (glm::distance(e1, glm::vec4{0, 0, 0, 0}) < 0.0001f) {
+        throw std::runtime_error("invalid over vector");
+    }
+
+    // calculate e0 basis vector, the 4d orthogonal vector to the other 3 bases
+    glm::vec4 e0 = cross4(e3, e2, e1);
+    e0 = glm::normalize(e0);
+
+    return {e2, e1, e0, e3};
+}
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