On 07/14/2013 09:34 PM, Andy Li wrote: > Hi, > > I have some questions on the OSMesa code. > As you suggested, I have continue looking into the swrast code. > However, I have trouble figuring out how the code works exactly. > Now I am now only focusing on the functions which draw lines. > As I look into s_lines.c, I saw the _swrast_choose_line(). > And depends on different cases, it will call > > _swrast_choose_aa_line_function(ctx) > or > USE(general_line) > or > USE(rgba_line) > or > USE(simple_no_z_rgba_line) > etc. > > The first thing I did is looking into the > _swrast_choose_aa_line_function() and it direct me to s_aaline.c > In that file, I saw the struct of LineInfo and other computation > functions for plane. > Then I looked at the _swrast_choose_aa_line_function() > > and when I saw the code: > swrast->Line = aa_general_rgba_line; > and > swrast->Line = aa_rgba_line; > > I am not sure what do they mean. And I won't be able to continue finding > useful info.
aa_rgba_line() drawns a "simple" RGBA antialiased line while aa_general_rgba_line() also computes texture coords, fog coord, etc. > I think the main problem I am having is I am not sure what are the steps > OSMesa have to take in order to draw a line into the frame buffer. > Would you be able to explain a bit on that? (what are the steps OSMesa > have to take in order to draw a line into the frame buffer?) > Does drawing a line involve computing the plane? AA lines are drawn by drawing a quadrilateral and computing pixel coverage involves computing plane equations. > What do s_aaline.c and s_aalinetemp.h actually mean? the "temp" files contain template code that's re-used multiple times in the .c file. > What is USE(general_line) ? Where is USE() define? grep "define USE" src/mesa/swrast/*.[ch] > What is swrast->Line = aa_general_rgba_line;? swrast->Line is a function pointer that points to the current line drawing function. The function is chosen by examining current GL rasterization state. > Would you suggest any debugging tool for me so that I can trace which > functions are called while the program is running? > For example I have the code below: > glBegin(GL_LINES); > glVertex3f(0.0, 0.0, 0.0); > glVertex3f(15, 0, 0); > glEnd(); > Is there any debugging tool which can trace glVertex3f back in the > library and see how OSMesa works? > I have tried using gdb, however, it would only by-pass the call the go > to the next command. You'll need to build mesa for debugging (CFLAGS="-g -O0" --enable-debug). But I don't really have time to explain all the nuances of debugging/tracing in Mesa. I'm not sure that'd really help you anyway. In general, when you drawing points/lines/triangles the s_points.c or s_lines.c or s_triangle.c code winds up calling _swrast_write_rgba() span. This function does Z testing, texturing, stippling, etc before calling a "put_pixels" or "put_row" function. Those functions call a "pack" function to pack an array of RGBA ubyte/float values into the framebuffer. Packing involves converting a canonical RGBA format into a specific pixel format, like RGBA8888, or RGB565, etc. The color buffer address, stride, etc. is obtained earlier through a call to ctx->Driver.MapRenderbuffer(). In the case of OSMesa, the color buffer is ordinary malloc'd memory that the user allocated. -Brian _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
