WIP camera stuff. Missing some useful quaternion helpers.

example/src/Entity.h

@@ -23,7 +23,40 @@ public:
 
     RenderComponent *renderComponent = NULL;
 
+    struct CameraInfo {
+        float fov = 90.0f;
+        float aspect = 1024.0f / 768.0f;
+        float near = 0.1f;
+        float far = 100.0f;
+    };
+    CameraInfo camera;
+
+    hmm_mat4 projectionMatrix() {
+        return HMM_Perspective(camera.fov, camera.aspect, camera.near, camera.far);
+    }
+
+    hmm_mat4 viewMatrix() {
+        return HMM_LookAt(worldPosition(), worldPosition() + forward(), up());
+    }
+
+    hmm_vec3 worldPosition() {
+        return (modelMatrix * HMM_Vec4(0.0f, 0.0f, 0.0f, 1.0f)).XYZ;
+    }
+
+    hmm_vec3 up() {
+        return (modelMatrix * HMM_Vec4(0.0f, 1.0f, 0.0f, 1.0f)).XYZ - worldPosition();
+    }
+
+    hmm_vec3 forward() {
+        return (modelMatrix * HMM_Vec4(1.0f, 0.0f, 0.0f, 1.0f)).XYZ - worldPosition();
+    }
+
+    hmm_vec3 right() {
+        return (modelMatrix * HMM_Vec4(0.0f, 0.0f, 1.0f, 1.0f)).XYZ - worldPosition();
+    }
+
     // Context for rendering and stuff
+    hmm_mat4 parentModelMatrix;
     hmm_mat4 modelMatrix;
 };
 

example/src/FollowCam.h

@@ -0,0 +1,58 @@
+#include <stdio.h>
+
+#ifndef HMME_FOLLOWCAM_H
+#define HMME_FOLLOWCAM_H
+
+#include "Entity.h"
+#include "HandmadeMath.h"
+
+class FollowCam : public Entity {
+public:
+    Entity *target;
+
+    FollowCam(Entity *t) {
+        target = t;
+    }
+
+    // HI BEN HERE IS YOUR STREAM OF CONSCIOUSNESS
+    // 
+    // Up is wonky. Really this whole thing is a little wonky, although it's
+    // gotten pretty close. You need to figure out how to directly calculate the
+    // axis and angle so you don't have to do this in two steps. Then it should
+    // Just Work.
+    // 
+    // Although you may have to figure out how to make the camera keep a consistent up vector.
+    // 
+    // Actually that shouldn't be too hard, because once you have a quaternion
+    // LookAt thing, you can just always pass world up to it.
+
+    void Tick(float deltaSeconds) override {
+        // rotation = HMM_QuaternionFromAxisAngle(target->worldPosition() - worldPosition(), 0.0f);
+        // rotation = HMM_QuaternionFromAxisAngle(HMM_Vec3(0.0f, 1.0f, 0.0f), HMM_ToRadians(0.0f));
+        // rotation = HMM_Qu
+        
+        hmm_vec3 fwd = (parentModelMatrix * HMM_Vec4(1.0f, 0.0f, 0.0f, 0.0f)).XYZ;
+        hmm_vec3 up = (parentModelMatrix * HMM_Vec4(0.0f, 1.0f, 0.0f, 0.0f)).XYZ;
+        hmm_vec3 to = target->worldPosition() - worldPosition();
+        float dot = HMM_DotVec3(fwd, HMM_NormalizeVec3(to));
+
+        if (HMM_ABS(dot - 1.0f) < 0.000001f) {
+            // do nothing to the rotation
+        } else if (HMM_ABS(dot + 1.0f) < 0.000001f) {
+            // rotate 180 I guess but for now do nothing
+        } else {
+            hmm_vec3 cross = HMM_Normalize(HMM_Cross(fwd, to));
+
+            rotation = HMM_QuaternionFromAxisAngle(    
+                cross,
+                HMM_ACOSF(dot)
+            );
+            rotation *= HMM_QuaternionFromAxisAngle(
+                HMM_Vec3(1.0f, 0.0f, 0.0f),
+                -HMM_ACOSF(HMM_DotVec3(cross, up))
+            );
+        }
+    }
+};
+
+#endif

example/src/main.cpp

@@ -11,6 +11,7 @@
 #include "Entity.h"
 #include "Cube.h"
 #include "MeshRenderComponent.h"
+#include "FollowCam.h"
 
 void TickTree(Entity *e, float deltaSeconds);
 void ComputeModelMatrices(Entity *ep, hmm_mat4 parentModelMatrix);
@@ -67,17 +68,27 @@ int main()
     // Accept fragment if it closer to the camera than the former one
     glDepthFunc(GL_LESS);
 
-    Cube root = Cube();
+    Cube c1 = Cube();
 
-    Entity child = Entity();
+    Entity monkey = Entity();
-    child.position = HMM_Vec3(2.1f, 0.0f, 0.0f);
+    monkey.position = HMM_Vec3(2.1f, 0.0f, 0.0f);
-    child.renderComponent = new MeshRenderComponent("MonkeySmooth.obj");
+    monkey.renderComponent = new MeshRenderComponent("MonkeySmooth.obj");
+
+    FollowCam cam = FollowCam(&monkey);
+    // cam.position = HMM_Vec3(3.0f, 3.0f, 4.0f);
+    cam.position = HMM_Vec3(3.0f, 3.0f, 5.0f);
+    // cam.rotation = HMM_QuaternionFromAxisAngle(HMM_Vec3(0.0f, 1.0f, 0.0f), HMM_ToRadians(90.0f));
 
     // Cube c = Cube();
-    // child.position = HMM_Vec3(2.1f, 0.0f, 0.0f);
+    // monkey.position = HMM_Vec3(2.1f, 0.0f, 0.0f);
 
-    // child.AddChild(&c);
+    // monkey.AddChild(&c);
-    root.AddChild(&child);
+    
+    c1.AddChild(&monkey);
+
+    Entity root = Entity();
+    root.AddChild(&c1);
+    root.AddChild(&cam);
 
     bool hasTicked = false;
     high_resolution_clock::time_point lastTickTime;
@@ -85,10 +96,6 @@ int main()
     do {
         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
-        hmm_mat4 projection = HMM_Perspective(90.0f, 1024.0f / 768.0f, 0.1f, 100.0f);
-        hmm_mat4 view = HMM_LookAt(HMM_Vec3(3.0f, 3.0f, 4.0f), HMM_Vec3(0.0f, 0.0f, 0.0f), HMM_Vec3(0.0f, 1.0f, 0.0f));
-        hmm_mat4 vp = projection * view;
-
         // Tick
         auto now = high_resolution_clock::now();
         if (hasTicked) {
@@ -103,6 +110,10 @@ int main()
         ComputeModelMatrices(&root, HMM_Mat4d(1.0f));
 
         // Render!
+        hmm_mat4 projection = cam.projectionMatrix();
+        hmm_mat4 view = cam.viewMatrix();
+        hmm_mat4 vp = projection * view;
+
         auto it = EntityIterator(&root);
         while (it.HasNext()) {
             Entity *e = it.Next();
@@ -142,6 +153,7 @@ void TickTree(Entity *e, float deltaSeconds) {
 }
 
 void ComputeModelMatrices(Entity *e, hmm_mat4 parentModelMatrix) {
+    e->parentModelMatrix = parentModelMatrix;
     e->modelMatrix = parentModelMatrix * HMM_Translate(e->position) * HMM_QuaternionToMat4(e->rotation) * HMM_Scale(e->scale);
 
     for (int i = 0; i < e->children.size(); i++) {