It's pretty easy to set up a simple camera that way. The player moves relative to the camera so you pan the camera as the player moves left and right rather than have the camera controlled by the mouse. This may not be the best code to do the job but it works:

Code:

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	IF (key_w == 1 && key_s == 0 && key_a == 0 && key_d == 0) { temp.x = camera.pan; }
	IF (key_s == 1 && key_w == 0 && key_a == 0 && key_d == 0) { temp.x = camera.pan + 180; }
	IF (key_a == 1 && key_s == 0 && key_w == 0 && key_d == 0) { temp.x = camera.pan + 90; camera.pan += 5 * time; }
	IF (key_d == 1 && key_s == 0 && key_a == 0 && key_w == 0) { temp.x = camera.pan - 90; camera.pan -= 5 * time; }
	IF (key_w == 1 && key_a == 1 && key_d == 0 && key_s == 0) { temp.x = camera.pan + 45; camera.pan += 2.5 * time; }
	IF (key_w == 1 && key_d == 1 && key_a == 0 && key_s == 0) { temp.x = camera.pan - 45; camera.pan -= 2.5 * time; }
	IF (key_s == 1 && key_a == 1 && key_d == 0 && key_w == 0) { temp.x = camera.pan + 135; camera.pan += 6 * time; }
	IF (key_s == 1 && key_d == 1 && key_a == 0 && key_w == 0) { temp.x = camera.pan - 135; camera.pan -= 6 * time; }

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Use that concept, introduce some new variables and you can set up a camera like that pretty easily if you have the experience.