Improve window resizing/scaling behavior

[SuperFromND]

I recently added the ability for Ikemen GO's window to be resized independently of game resolution similar to how MUGEN 1.1/SDL handles its game window. The problem is, the way I implemented it is quite literally just calling gl.Viewport to resize and offset the viewport to fit the window. This works, but it's not ideal and doesn't behave like how other programs would do it (taking the frame and projecting it onto a texture, then rendering that texture to the screen; doing it this way gives essentially free filtering as well as properly working with shaders, something the viewport approach breaks :<).

If I was just a bit more savvy with OpenGL, this could probably be pretty easy to do, but I figured I'd throw it out here in the discussions channel just in case someone in internet-land who knows OpenGL better stumbles across it. 👍

[SuperFromND]

Trying to improve it myself, this modded version of EndFrame() almost works:

func (r *Renderer) EndFrame() {
	if sys.multisampleAntialiasing {
		gl.BindFramebuffer(gl.DRAW_FRAMEBUFFER, r.fbo_f)
		gl.BindFramebuffer(gl.READ_FRAMEBUFFER, r.fbo)
		gl.BlitFramebuffer(0, 0, sys.scrrect[2], sys.scrrect[3], 0, 0, sys.scrrect[2], sys.scrrect[3], gl.COLOR_BUFFER_BIT, gl.LINEAR)
	}

	x, y, resizedWidth, resizedHeight := sys.window.GetScaledViewportSize()

	postShader := r.postShaderSelect[sys.postProcessingShader]

	gl.Clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)
	gl.UseProgram(postShader.program)
	gl.Disable(gl.BLEND)

	gl.ActiveTexture(gl.TEXTURE0)
	if sys.multisampleAntialiasing {
		gl.BindTexture(gl.TEXTURE_2D, r.fbo_f_texture.handle)
	} else {
		gl.BindTexture(gl.TEXTURE_2D, r.fbo_texture)
	}
	gl.Uniform1i(postShader.u["Texture"], 0)
	gl.Uniform2f(postShader.u["TextureSize"], float32(sys.scrrect[2]), float32(sys.scrrect[3]))

	gl.BindBuffer(gl.ARRAY_BUFFER, r.postVertBuffer)

	loc := r.modelShader.a["VertCoord"]
	gl.EnableVertexAttribArray(uint32(loc))
	gl.VertexAttribPointerWithOffset(uint32(loc), 2, gl.FLOAT, false, 0, 0)

	gl.DrawArrays(gl.TRIANGLE_STRIP, 0, 4)

	gl.DisableVertexAttribArray(uint32(loc))
	gl.Viewport(x, y, resizedWidth, resizedHeight)
	gl.BindFramebuffer(gl.READ_FRAMEBUFFER, r.fbo_texture)
	gl.BindFramebuffer(gl.DRAW_FRAMEBUFFER, 0)
	gl.BlitFramebuffer(0, 0, sys.scrrect[2], sys.scrrect[3], x, y, x+resizedWidth, y+resizedHeight, gl.COLOR_BUFFER_BIT, gl.LINEAR)
}

The result almost works, but exhibits pretty severe corruption (likely as a result of reading r.fbo_texture directly) and it doesn't scale at all if MSAA is turned on (giving solid black when attempting to scale, but working when only one dimension is resized).

[SuperFromND]

Just now found out removing the gl.Clear command at least somewhat mitigates the corruption, but it still remains. :<

According to RenderDoc, the actual underlying texture is fine, just the part where it gets drawn to the screen is malfunctioning. Which means either gl.Viewport or gl.BlitFramebuffer is the cause of the problem.

[SuperFromND]

#1895 should now address these problems. 👍

[Kiwi1444]

Is there any chance that IkemenGo will remember the position and size of the window?