/** Creates a perspective projection matrix suitable for 2D and 3D rendering.
*
* <p>The first 4 parameters define which area of the stage you want to view (the camera
* will 'zoom' to exactly this region). The final 3 parameters determine the perspective
* in which you're looking at the stage.</p>
*
* <p>The stage is always on the rectangle that is spawned up between x- and y-axis (with
* the given size). All objects that are exactly on that rectangle (z equals zero) will be
* rendered in their true size, without any distortion.</p>
*
* <p>If you pass only the first 4 parameters, the camera will be set up above the center
* of the stage, with a field of view of 1.0 rad.</p>
*/
public static Matrix3D CreatePerspectiveProjectionMatrix(
float x, float y, float width, float height,
float stageWidth = 0f, float stageHeight = 0f, float[] cameraPos = null)
{
Matrix3D outMatrix = Matrix3D.Create();
if (stageWidth <= 0)
{
stageWidth = width;
}
if (stageHeight <= 0)
{
stageHeight = height;
}
if (cameraPos == null)
{
cameraPos = new[] {
stageWidth / 2f, stageHeight / 2f, // -> center of stage
stageWidth / (float)Math.Tan(0.5f) * 0.5f
}; // -> fieldOfView = 1.0 rad
}
float focalLength = Math.Abs(cameraPos[2]);
float offsetX = cameraPos[0] - stageWidth / 2f;
float offsetY = cameraPos[1] - stageHeight / 2f;
float far = focalLength * 20f;
const float near = 1f;
float scaleX = stageWidth / width;
float scaleY = stageHeight / height;
// set up general perspective
float[] sMatrixData = new float[16];
sMatrixData[0] = 2 * focalLength / stageWidth; // 0,0
sMatrixData[5] = -2 * focalLength / stageHeight; // 1,1 [negative to invert y-axis]
sMatrixData[10] = far / (far - near); // 2,2
sMatrixData[14] = -far * near / (far - near); // 2,3
sMatrixData[11] = 1; // 3,2
// now zoom in to visible area
sMatrixData[0] *= scaleX;
sMatrixData[5] *= scaleY;
sMatrixData[8] = scaleX - 1 - 2 * scaleX * (x - offsetX) / stageWidth;
sMatrixData[9] = -scaleY + 1 + 2 * scaleY * (y - offsetY) / stageHeight;
outMatrix.CopyRawDataFrom(sMatrixData);
outMatrix.PrependTranslation(
-stageWidth / 2.0f - offsetX,
-stageHeight / 2.0f - offsetY,
focalLength);
return(outMatrix);
}
