Dart Documentationbox2d_browserCanvasViewportTransform

CanvasViewportTransform class

class CanvasViewportTransform extends IViewportTransform {
 static const int DEFAULT_DRAWING_SCALE = 20;

 /**
  * Constructs a new viewport transform with the default scale.
  */
 CanvasViewportTransform(Vector _extents, Vector _center) :
   super(_extents, _center, DEFAULT_DRAWING_SCALE) {
   yFlip = true;
 }

 /**
  * Sets the rendering context such that all drawing commands given in terms
  * of the world coordinate system will display correctly on the canvas screen.
  */
 void updateTransformation(CanvasRenderingContext2D ctx) {
   // Clear all previous transformation.
   ctx.setTransform(1,0,0,1,0,0);

   // Translate to the center of the canvas screen. This will be considered the
   // actual origin.
   ctx.translate(extents.x, extents.y);

   // Translate to account for the currently applied translation.
   ctx.translate(translation.x, translation.y);

   // Scale everything according to the current scale and mirror the y-axis.
   ctx.scale(scale, -scale);
 }

}

Extends

IViewportTransform > CanvasViewportTransform

Static Properties

const int DEFAULT_DRAWING_SCALE #

static const int DEFAULT_DRAWING_SCALE = 20;

Constructors

new CanvasViewportTransform(Vector _extents, Vector _center) #

Constructs a new viewport transform with the default scale.

CanvasViewportTransform(Vector _extents, Vector _center) :
 super(_extents, _center, DEFAULT_DRAWING_SCALE) {
 yFlip = true;
}

Properties

Vector center #

inherited from IViewportTransform

center of the viewport.

Vector center;

Vector extents #

inherited from IViewportTransform

This is the half-width and half-height. This should be the actual half-width and half-height, not anything transformed or scaled.

Vector extents;

num scale #

inherited from IViewportTransform

Returns the scaling factor used in converting from world sizes to rendering sizes.

num scale;

Vector translation #

inherited from IViewportTransform

The current translation is the difference in canvas units between the actual center of the canvas and the currently specified center. For example, if the actual canvas center is (5, 5) but the current center is (6, 6), the translation is (1, 1).

Vector get translation {
 Vector result = new Vector.copy(extents);
 result.subLocal(center);
 return result;
}
void set translation(Vector translation) {
 center.setFrom(extents);
 center.subLocal(translation);
}

bool yFlip #

inherited from IViewportTransform

if we flip the y axis when transforming.

bool yFlip;

Methods

void getScreenToWorld(Vector argScreen, Vector argWorld) #

inherited from IViewportTransform

Takes the screen coordinates (argScreen) and puts the corresponding world coordinates in argWorld. It should be safe to give the same object as both parameters.

void getScreenToWorld(Vector argScreen, Vector argWorld) {
 num translationCorrectedX = argScreen.x - translation.x;
 num translationCorrectedY = argScreen.y + translation.y;

 num gridCorrectedX = (translationCorrectedX - extents.x) / scale;
 num gridCorrectedY = ((translationCorrectedY - extents.y) * -1) / scale;
 argWorld.setCoords(gridCorrectedX, gridCorrectedY);
}

void getWorldToScreen(Vector argWorld, Vector argScreen) #

inherited from IViewportTransform

Takes the world coordinate (argWorld) puts the corresponding screen coordinate in argScreen. It should be safe to give the same object as both parameters.

void getWorldToScreen(Vector argWorld, Vector argScreen) {
 // Correct for canvas considering the upper-left corner, rather than the
 // center, to be the origin.
 num gridCorrectedX = (argWorld.x * scale) + extents.x;
 num gridCorrectedY = extents.y - (argWorld.y * scale);

 argScreen.setCoords(gridCorrectedX + translation.x, gridCorrectedY +
     -translation.y);
}

void setCamera(num x, num y, num s) #

inherited from IViewportTransform

Sets the transform's center to the given x and y coordinates, and using the given scale.

void setCamera(num x, num y, num s) {
 center.setCoords(x, y);
 scale = s;
}

void updateTransformation(CanvasRenderingContext2D ctx) #

Sets the rendering context such that all drawing commands given in terms of the world coordinate system will display correctly on the canvas screen.

void updateTransformation(CanvasRenderingContext2D ctx) {
 // Clear all previous transformation.
 ctx.setTransform(1,0,0,1,0,0);

 // Translate to the center of the canvas screen. This will be considered the
 // actual origin.
 ctx.translate(extents.x, extents.y);

 // Translate to account for the currently applied translation.
 ctx.translate(translation.x, translation.y);

 // Scale everything according to the current scale and mirror the y-axis.
 ctx.scale(scale, -scale);
}