Populate 2,3 of viewport matrix with 1s, use look-at call to project onto model

Author: Michael Bassili

our_gl.cpp

@@ -13,10 +13,10 @@ void viewport(int x, int y, int w, int h) {
     Viewport = Matrix::identity();
     Viewport[0][3] = x+w/2.f;
     Viewport[1][3] = y+h/2.f;
-    Viewport[2][3] = depth/2.f;
+    Viewport[2][3] = 1.f;
     Viewport[0][0] = w/2.f;
     Viewport[1][1] = h/2.f;
-    Viewport[2][2] = depth/2.f;
+    Viewport[2][2] = 0;
 }
 
 void projection(float coeff) {
@@ -28,13 +28,15 @@ void lookat(Vec3f eye, Vec3f center, Vec3f up) {
     Vec3f z = (eye-center).normalize();
     Vec3f x = cross(up,z).normalize();
     Vec3f y = cross(z,x).normalize();
-    ModelView = Matrix::identity();
+    Matrix Minv = Matrix::identity();
+    Matrix Tr   = Matrix::identity();
     for (int i=0; i<3; i++) {
-        ModelView[0][i] = x[i];
-        ModelView[1][i] = y[i];
-        ModelView[2][i] = z[i];
-        ModelView[i][3] = -center[i];
+        Minv[0][i] = x[i];
+        Minv[1][i] = y[i];
+        Minv[2][i] = z[i];
+        Tr[i][3] = -center[i];
     }
+    ModelView = Minv*Tr;
 }
 
 Vec3f barycentric(Vec2f A, Vec2f B, Vec2f C, Vec2f P) {
@@ -50,25 +52,30 @@ Vec3f barycentric(Vec2f A, Vec2f B, Vec2f C, Vec2f P) {
     return Vec3f(-1,1,1); // in this case generate negative coordinates, it will be thrown away by the rasterizator
 }
 
-void triangle(Vec4f *pts, IShader &shader, TGAImage &image, float *zbuffer) {
+void triangle(mat<4,3,float> &clipc, IShader &shader, TGAImage &image, float *zbuffer) {
+    mat<3,4,float> pts  = (Viewport*clipc).transpose(); // transposed to ease access to each of the points
+    mat<3,2,float> pts2;
+    for (int i=0; i<3; i++) pts2[i] = proj<2>(pts[i]/pts[i][3]);
+
     Vec2f bboxmin( std::numeric_limits<float>::max(),  std::numeric_limits<float>::max());
     Vec2f bboxmax(-std::numeric_limits<float>::max(), -std::numeric_limits<float>::max());
+    Vec2f clamp(image.get_width()-1, image.get_height()-1);
     for (int i=0; i<3; i++) {
         for (int j=0; j<2; j++) {
-            bboxmin[j] = std::min(bboxmin[j], pts[i][j]/pts[i][3]);
-            bboxmax[j] = std::max(bboxmax[j], pts[i][j]/pts[i][3]);
+            bboxmin[j] = std::max(0.f,      std::min(bboxmin[j], pts2[i][j]));
+            bboxmax[j] = std::min(clamp[j], std::max(bboxmax[j], pts2[i][j]));
         }
     }
     Vec2i P;
     TGAColor color;
     for (P.x=bboxmin.x; P.x<=bboxmax.x; P.x++) {
         for (P.y=bboxmin.y; P.y<=bboxmax.y; P.y++) {
-            Vec3f c = barycentric(proj<2>(pts[0]/pts[0][3]), proj<2>(pts[1]/pts[1][3]), proj<2>(pts[2]/pts[2][3]), proj<2>(P));
-            float z = pts[0][2]*c.x + pts[1][2]*c.y + pts[2][2]*c.z;
-            float w = pts[0][3]*c.x + pts[1][3]*c.y + pts[2][3]*c.z;
-            int frag_depth = z/w;
-            if (c.x<0 || c.y<0 || c.z<0 || zbuffer[P.x+P.y*image.get_width()]>frag_depth) continue;
-            bool discard = shader.fragment(c, color);
+            Vec3f bc_screen  = barycentric(pts2[0], pts2[1], pts2[2], P);
+            Vec3f bc_clip    = Vec3f(bc_screen.x/pts[0][3], bc_screen.y/pts[1][3], bc_screen.z/pts[2][3]);
+            bc_clip = bc_clip/(bc_clip.x+bc_clip.y+bc_clip.z);
+            float frag_depth = clipc[2]*bc_clip;
+            if (bc_screen.x<0 || bc_screen.y<0 || bc_screen.z<0 || zbuffer[P.x+P.y*image.get_width()]>frag_depth) continue;
+            bool discard = shader.fragment(Vec3f(P.x, P.y, frag_depth), bc_clip, color);
             if (!discard) {
                 zbuffer[P.x+P.y*image.get_width()] = frag_depth;
                 image.set(P.x, P.y, color);

our_gl.h

@@ -4,9 +4,8 @@
 #include "geometry.h"
 
 extern Matrix ModelView;
-extern Matrix Viewport;
 extern Matrix Projection;
-const float depth = 2000.f;
+extern Matrix Viewport;
 
 void viewport(int x, int y, int w, int h);
 void projection(float coeff=0.f); // coeff = -1/c
@@ -15,9 +14,10 @@ void lookat(Vec3f eye, Vec3f center, Vec3f up);
 struct IShader {
     virtual ~IShader();
     virtual Vec4f vertex(int iface, int nthvert) = 0;
-    virtual bool fragment(Vec3f bar, TGAColor &color) = 0;
+    virtual bool fragment(Vec3f gl_FragCoord, Vec3f bar, TGAColor &color) = 0;
 };
 
-void triangle(Vec4f *pts, IShader &shader, TGAImage &image, float *zbuffer);
+//void triangle(Vec4f *pts, IShader &shader, TGAImage &image, float *zbuffer);
+void triangle(mat<4,3,float> &pts, IShader &shader, TGAImage &image, float *zbuffer);
 #endif //__OUR_GL_H__