[NaCl SDK] Earth demo modifications for gonacl PNaCl.

native_client_sdk/src/examples/demo/earth/earth.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <assert.h>
 #include <math.h>
 #include <ppapi/c/ppb_input_event.h>
 #include <ppapi/cpp/input_event.h>
 #include <ppapi/cpp/var.h>
 #include <ppapi/cpp/var_array.h>
@@ skipping 365 matching lines @@
   return ps_context_->data + x + y * ps_context_->stride / sizeof(uint32_t);
 }
 
 // This is the meat of the ray tracer.  Given a pixel span (x0, x1) on
 // scanline y, shoot rays into the scene and render what they hit.  Use
 // scanline coherence to do a few optimizations
 void Planet::wRenderPixelSpan(int x0, int x1, int y) {
   if (!base_tex_ || !night_tex_)
     return;
   const int kColorBlack = MakeRGBA(0, 0, 0, 0xFF);
+  float width = ps_context_->width;
+  float height = ps_context_->height;
+  float min_dim = width < height ? width : height;
+  float offset_x = width < height ? 0 : (width - min_dim) * 0.5f;
+  float offset_y = width < height ? (height - min_dim) * 0.5f : 0;
   float y0 = eye_y_;
   float z0 = eye_z_;
-  float y1 = (static_cast<float>(y) / ps_context_->height) * 2.0f - 1.0f;
+  float y1 = (static_cast<float>(y - offset_y) / min_dim) * 2.0f - 1.0f;
   float z1 = 0.0f;
   float dy = (y1 - y0);
   float dz = (z1 - z0);
   float dy_dy_dz_dz = dy * dy + dz * dz;
   float two_dy_y0_y_two_dz_z0_z = 2.0f * dy * (y0 - planet_y_) +
                                   2.0f * dz * (z0 - planet_z_);
   float planet_xyz_eye_xyz = planet_xyz_ + eye_xyz_;
   float y_y0_z_z0 = planet_y_ * y0 + planet_z_ * z0;
-  float oowidth = 1.0f / ps_context_->width;
+  float oowidth = 1.0f / min_dim;
   uint32_t* pixels = this->wGetAddr(x0, y);
   for (int x = x0; x <= x1; ++x) {
     // scan normalized screen -1..1
-    float x1 = (static_cast<float>(x) * oowidth) * 2.0f - 1.0f;
+    float x1 = (static_cast<float>(x - offset_x) * oowidth) * 2.0f - 1.0f;
     // eye
     float x0 = eye_x_;
     // delta from screen to eye
     float dx = (x1 - x0);
     // build a, b, c
     float a = dx * dx + dy_dy_dz_dz;
     float b = 2.0f * dx * (x0 - planet_x_) + two_dy_y0_y_two_dz_z0_z;
     float c = planet_xyz_eye_xyz +
               -2.0f * (planet_x_ * x0 + y_y0_z_z0) - (planet_radius2_);
     // calculate discriminant
@@ skipping 372 matching lines @@
     // Do simulation, render and present.
     earth.Update();
   }
 
   return 0;
 }
 
 // Register the function to call once the Instance Object is initialized.
 // see: pappi_simple/ps_main.h
 PPAPI_SIMPLE_REGISTER_MAIN(example_main);