Created attachment 2714 [details]
clip test v2

After adding a test file to bug #2700, this bug popped up.
Completing the test file a little more, showed a few more rare use case problems.
I could split this up into multiple reports if needed,
copy-pasted from test file:
(note that proposed fixes have not been tested)
-----------------------

observed problems: (some of these have been reported)

-software render + viewport + clip_rectangle
	, test 3,4,7 and 8 show this.
+ bug ID #3612 (SDL_render_sw.c, line 368, SW_UpdateClipRect(): viewport offset is missing)

-software render + viewport + SDL_RenderReadPixels
	, the read offset is incorrect when a viewport is used
	, can test this with taking a screen shot from test 3,4,7 and 8.
+ (SDL_render_sw.c, line 842: viewport offset is added a second time)

-Windows 7 opengl + SDL_RenderReadPixels
	does NOT correspond to what is shown
	, looks like its always a frame behind
	, screen shots taken will be an image from the previous test... press 'r' to force a repaint
+ ?Related? bug ID #3619 (different OS, debian did gave correct results for me)

-SDL_SetRenderTarget(ren, target) + logical size
	a logical size is set by default
	, test 4 and 6 shows this, a logical-size is detected and used as a backup (line 212 in here)
	, only the first time it is drawn correctly, press 'r' to refresh
+ (SDL_render.c, line 1124: renderer->logical_w/h should be initialized to 0, not the texture->w/h)

-opengl(es2) render + scale
	default render and target texture give different visual results
	, test 5,6 and 7,8 show this.
+ 


Draw primitives problems:
note : SDL_RenderDrawRect() bugs are SDL_RenderDrawLines(multiple lines) bugs in reality.

direct3d - windows {
- SDL_RenderDrawRect
	top-left + bottom-left pixels are drawn 2 times
}
software - all {
- SDL_RenderDrawLine
	1 pixel lines are not drawn
}
opengl(es2) - debian 8 {
- SDL_RenderDrawLine
	1 pixel lines are not drawn (gles2 does draw them)
- SDL_RenderDrawRect
	bottom-left pixel is drawn 2 times
	bottom-right pixel is NOT always drawn
}
all - renderers - tested {
- SDL_RenderDrawRect
	0*0 width/height draws a negative 2*2 rectangle
	1*1 width/height is not drawn
+ SDL_RenderDrawRect() probably needs a few special checks...
}

I missed a few :


software render + SDL_RenderFillRect
	A w or h with 0 will always MAX() up to 1 - SW_RenderFillRects() uses MAX(w/h,1)
	, tests 1 and 2 show this

software render + viewport + clip-rect
	It seems the software renderer is using SDL_SetClipRect(), to set the viewport
	, this results in broken behavior if the clip-rect is used in combination with a viewport.
	, adding any draw call after the clip-rectangle usage in the test file, will ignore viewport settings and draw anywhere.

Bug #3324 has a patch to fix the SDL_RenderReadPixels problem with software renderer.