Screen::Screen(const CmdArgs &args)
: _width(args.width()), _height(args.height()) {
// Read the input file.
std::string input = args.inputFilename();
std::ifstream in(input);
stop_if(!in.is_open(), "failed to open input file (%s).", input.c_str());
Point camera, center;
Vector up, right;
float fovy;
in >> camera.x >> camera.y >> camera.z;
in >> center.x >> center.y >> center.z;
in >> up.x >> up.y >> up.z;
in >> fovy;
// Camera direction to the center of the screen..
Vector dir = (center - camera).normalize();
// Make up orthogonal to the camera direction.
up -= Vector::proj(dir, up);
up.normalize();
// Calculate the right direction.
right = Vector::cross(dir, up);
// Calculate the width and height of the screen.
float d = Point::distance(center, camera);
_heightSize = 2 * tan(toRads(fovy / 2.0f)) * d;
_widthSize = (_heightSize * _width) / _height;
// Save the top left pixel.
Point topLeft = center - (right * (_widthSize / 2)) + (up * (_heightSize / 2));
_topLeftPixelPos[0] = topLeft.x;
_topLeftPixelPos[1] = topLeft.y;
_topLeftPixelPos[2] = topLeft.z;
_topLeftPixelPos[3] = 1.0f;
_cameraPos[0] = camera.x;
_cameraPos[1] = camera.y;
_cameraPos[2] = camera.z;
_cameraPos[3] = 1.0f;
_upVector[0] = up.x;
_upVector[1] = up.y;
_upVector[2] = up.z;
_upVector[3] = 0.0f;
_rightVector[0] = right.x;
_rightVector[1] = right.y;
_rightVector[2] = right.z;
_rightVector[3] = 0.0f;
// If the distance from the camera to the center of the screen is d and
// half the fovy is f, the maximum height of the screen is:
// A schematic (from the side);
// .
// . |
// . | <- h
// . |
// . f |
// Camera -> .----------------. <- Screen center
// . ^d |
// . |
// . | <- h
// . |
// .
// tan(f) = h/d => h = tan(f) * d;
// The height of the screen is h = tan(f) * d.
//
// The we know that if the screen has n pixels from top to low (2h), then
// 2h ~ n
// The width 2w of the screen, with m pixels, is:
// 2w ~ m
// Then 2w = (2h*m)/n
}
