author Sam Lantinga <>
Thu, 01 Aug 2013 09:15:36 -0700
changeset 7563 c128ed448c30
parent 7338 9962dfd88567
child 8849 1c2c95a5b033
permissions -rw-r--r--
Fixed bug 1968 - SDL_RenderCopy stretch loses proportion on viewport boundaries for 3D renderers


SDL_RenderCopy clips dstrect against the viewport. Then it adjusts the
srcrect by "appropriate" amount of pixels. This amount is actually
wrong, quite a lot, because of the rounding errors introduced in the "*
factor / factor" scale.

real_srcrect.x += (deltax * real_srcrect.w) / dstrect->w;
real_srcrect.w += (deltaw * real_srcrect.w) / dstrect->w;

For example:

I have a 32 x 32 srcrect and a 64 x 64 dstrect. So far the
stretching is done perfectly, by a factor of 2.

Now, consider dstrect being clipped against the viewport, so it becomes
56 x 64. Now, the factor becomes 1.75 ! The adjustment to "srcrect"
can't handle this, cause srcrect is in integers.

And thus we now have incorrect mapping, with dstrect not being in the
right proportion to srcrect.

The problem is most evident when upscaling stuff, like displaying a 8x8
texture with a zoom of 64 or more, and moving it beyond the corners of
the screen. It *looks* really really bad.

Note: RenderCopyEX does no such clipping, and is right to do so. The fix would be to remove any such clipping from RenderCopy too. And then fix the software renderer, because it has the same fault, independently of RenderCopy.

[attached patch]
this leaves Software Renderer buggy, as it does it's own clipping later on
     1 <HTML>
     2 	<HEAD>
     3 		<TITLE>Using SDL with Microsoft Visual C++</TITLE>
     4 	</HEAD>
     5 	<BODY>
     6 		<H1>
     7 			Using SDL with Microsoft Visual C++
     8 		</H1>
     9 		<H3>
    10 			by <A HREF="">Lion Kimbro </A>and additions by <A HREF="">
    11 				James Turk</A>
    12 		</H3>
    13 		<p>
    14 			You can either use the precompiled libraries from <A HREF=""> the SDL Download web site </A>, or you can build SDL yourself.
    15 		</p>
    16 		<H3>
    17 			Building SDL
    18 		</H3>
    19 		<P>
    20 			Go into the VisualC directory and double-click on the Visual Studio solution for your version of Visual Studio, e.g. <CODE>SDL_VS2008.sln</CODE> This should open up the IDE.
    21 		</P>
    22 		<P>
    23 			There are different solution files for the various
    24 			versions of the IDE. Please use the appropiate version
    25 			2008, 2010 or 2012; the 2010EE and 2012EE files
    26 			should be used with the "Express Edition" releases.
    27 		</P>
    28 		<P>
    29 			Build the <CODE>.dll</CODE> and <CODE>.lib</CODE> files.
    30 		</P>
    31 		<P>
    32 			This is done by right clicking on each project in turn (Projects are listed in 
    33 			the Workspace panel in the FileView tab), and selecting "Build".
    34 		</P>
    35 		<P>
    36 			You may get a few warnings, but you should not get any errors. You do have to 
    37 			have at least the DirectX 9 SDK installed, however. The latest 
    38 			version of DirectX can be downloaded from <A HREF="">Microsoft</A>.
    39 		</P>
    40 		<P>
    41 			Later, we will refer to the following .lib and .dll files that have just been 
    42 			generated:
    43 		</P>
    44 		<ul>
    45     <li> SDL2.dll</li>
    46     <li> SDL2.lib</li>
    47     <li> SDL2main.lib</li>
    48     </ul>
    49 		<P>
    50 			Search for these using the Windows Find (Windows-F) utility inside the VisualC directory.
    51 		</P>
    52 		<H3>
    53 			Creating a Project with SDL
    54 		</H3>
    55 		<P>
    56 			Create a project as a Win32 Application.
    57 		</P>
    58 		<P>
    59 			Create a C++ file for your project.
    60 		</P>
    61 		<P>
    62 			Set the C runtime to "Multi-threaded DLL" in the menu: <CODE>Project|Settings|C/C++ 
    63 				tab|Code Generation|Runtime Library </CODE>.
    64 		</P>
    65 		<P>
    66 			Add the SDL <CODE>include</CODE> directory to your list of includes in the 
    67 			menu: <CODE>Project|Settings|C/C++ tab|Preprocessor|Additional include directories </CODE>
    68 			.
    69 			<br>
    70 			<STRONG><FONT color="#009900">VC7 Specific: Instead of doing this I find it easier to 
    71 					add the include and library directories to the list that VC7 keeps. Do this by 
    72 					selecting Tools|Options|Projects|VC++ Directories and under the "Show 
    73 					Directories For:" dropbox select "Include Files", and click the "New Directory 
    74 					Icon" and add the [SDLROOT]\include directory (e.g. If you installed to 
    75 					c:\SDL\ add c:\SDL\include).&nbsp;Proceed to&nbsp;change the 
    76 					dropbox selection to "Library Files" and add [SDLROOT]\lib.</FONT></STRONG>
    77 		</P>
    78 			<P>
    79 				The "include directory" I am referring to is the <CODE>include</CODE> folder 
    80 				within the main SDL directory (the one that this HTML file located within).
    81 			</P>
    82 			<P>
    83 				Now we're going to use the files that we had created earlier in the Build SDL 
    84 				step.
    85 			</P>
    86 			<P>
    87 				Copy the following files into your Project directory:
    88 			</P>
    89 			<ul>
    90      <li> SDL2.dll</li>
    91      </ul>
    92 			<P>
    93 				Add the following files to your project (It is not necessary to copy them to 
    94 				your project directory):
    95 			</P>
    96 			<ul>
    97      <li> SDL2.lib </li>
    98      <li> SDL2main.lib</li>
    99      </ul>
   100 			<P>
   101 				(To add them to your project, right click on your project, and select "Add 
   102 				files to project")
   103 			</P>
   104 		<P><STRONG><FONT color="#009900">Instead of adding the files to your project it is more 
   105 					desireable to add them to the linker options: Project|Properties|Linker|Command 
   106 					Line and type the names of the libraries to link with in the "Additional 
   107 					Options:" box.&nbsp; Note: This must be done&nbsp;for&nbsp;each&nbsp;build 
   108 					configuration (e.g. Release,Debug).</FONT></STRONG></P>
   109 		<H3>
   110 			SDL 101, First Day of Class
   111 		</H3>
   112 		<P>
   113 			Now create the basic body of your project. The body of your program should take 
   114 			the following form: <CODE>
   115 				<PRE>
   116 #include "SDL.h"
   118 int main( int argc, char* argv[] )
   119 {
   120   // Body of the program goes here.
   121   return 0;
   122 }
   123 </PRE>
   124 			</CODE>
   125 		<P></P>
   126 		<H3>
   127 			That's it!
   128 		</H3>
   129 		<P>
   130 			I hope that this document has helped you get through the most difficult part of 
   131 			using the SDL: installing it. Suggestions for improvements to this document 
   132 			should be sent to the writers of this document.
   133 		</P>
   134 		<P>
   135 			Thanks to Paulus Esterhazy (, for the work on VC++ port.
   136 		</P>
   137 		<P>
   138 			This document was originally called "VisualC.txt", and was written by <A HREF="">
   139 				Sam Lantinga</A>.
   140 		</P>
   141 		<P>
   142 			Later, it was converted to HTML and expanded into the document that you see 
   143 			today by <A HREF="">Lion Kimbro</A>.
   144 		</P>
   145 		<P>Minor Fixes and Visual C++ 7 Information (In Green) was added by <A HREF="">James Turk</A>
   146 		</P>
   147 	</BODY>
   148 </HTML>