[PATCH] glretrace: Add a new --stub-fs to stub out fragment shaders

[Carl Worth]

With this option, all fragment shaders will be replaced with a stub
shader that simply draws solid magenta. This can be useful for
measuring the time spent in all other portions of the pipeline.
---

 José Fonseca <jose.r.fonseca at gmail.com> writes:
 > One thing to watch out is that the vertex shader could be potentially
 > simplified because its outputs don't get used by the fragment shader.

 Sure. So we're back to "we really need better performance-measuring
 extensions" as we already agreed.

 > Concerning your change, would it be possible to use a
 > glGetShaderiv(GL_SHADER_TYPE) instead of the fragmentShaders set?

 Good idea. That's less code, so obviously better. See below.

 retrace/glretrace.py     |   30 ++++++++++++++++++++++++++++++
 retrace/retrace.hpp      |    5 +++++
 retrace/retrace_main.cpp |    8 ++++++--
 3 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/retrace/glretrace.py b/retrace/glretrace.py
index 08fc6a0..b22c0c0 100644
--- a/retrace/glretrace.py
+++ b/retrace/glretrace.py
@@ -289,10 +289,39 @@ class GlRetracer(Retracer):
             print r'    if (pipeline) {'
             print r'        _pipelineHasBeenBound = true;'
             print r'    }'
+
+        if function.name in ('glShaderSource', 'glShaderSourceARB'):
+            if (function.name == 'glShaderSource'):
+                shader_name = 'shader';
+            else:
+                shader_name = 'shaderObj';
+            print r'    if (retrace::stubFragmentShaders) {'
+            print r'        GLint shader_type;'
+            print r'        glGetShaderiv(%s, GL_SHADER_TYPE, &shader_type);' % (shader_name)
+            print r'        if (shader_type == GL_FRAGMENT_SHADER) {'
+            print r'            count = 1;'
+            print r'            string[0] = "#version 120\n\n"'
+            print r'                        "void main()\n"'
+            print r'                        "{\n"'
+            print r'                        "     /* Magenta! */\n"'
+            print r'                        "    gl_FragColor = vec4(1, 0, 1, 1);\n"'
+            print r'                        "}";'
+            print r'            length[0] = strlen(string[0]);'
+            print r'        }'
+            print r'    }'
         
         if function.name == 'glCreateShaderProgramv':
             # When dumping state, break down glCreateShaderProgramv so that the
             # shader source can be recovered.
+            print r'    if (retrace::stubFragmentShaders && type == GL_FRAGMENT_SHADER) {'
+            print r'        count = 1;'
+            print r'        strings[0] = "#version 120\n\n"'
+            print r'                     "void main()\n"'
+            print r'                     "{\n"'
+            print r'                     "     /* Magenta! */\n"'
+            print r'                     "    gl_FragColor = vec4(1, 0, 1, 1);\n"'
+            print r'                     "}";'
+            print r'    }'
             print r'    if (retrace::dumpingState) {'
             print r'        GLuint _shader = glCreateShader(type);'
             print r'        if (_shader) {'
@@ -477,6 +506,7 @@ class GlRetracer(Retracer):
 if __name__ == '__main__':
     print r'''
 #include <string.h>
+#include <set>
 
 #include "glproc.hpp"
 #include "glretrace.hpp"
diff --git a/retrace/retrace.hpp b/retrace/retrace.hpp
index 0ee0e55..be49156 100644
--- a/retrace/retrace.hpp
+++ b/retrace/retrace.hpp
@@ -152,6 +152,11 @@ extern bool profiling;
  */
 extern bool dumpingState;
 
+/**
+ * Stubbing out fragment shaders (to measure vertex shader contribution)
+ */
+extern bool stubFragmentShaders;
+
 
 extern bool doubleBuffer;
 extern bool coreProfile;
diff --git a/retrace/retrace_main.cpp b/retrace/retrace_main.cpp
index 093ab17..1538e0a 100644
--- a/retrace/retrace_main.cpp
+++ b/retrace/retrace_main.cpp
@@ -55,7 +55,7 @@ int verbosity = 0;
 bool debug = true;
 bool profiling = false;
 bool dumpingState = false;
-
+bool stubFragmentShaders = false;
 
 bool doubleBuffer = true;
 bool coreProfile = false;
@@ -290,7 +290,9 @@ usage(const char *argv0) {
         "  -S CALLSET   calls to snapshot (default is every frame)\n"
         "  -v           increase output verbosity\n"
         "  -D CALLNO    dump state at specific call no\n"
-        "  -w           waitOnFinish on final frame\n";
+        "  -w           waitOnFinish on final frame\n"
+        "  --stub-fs    Replace all fragment shaders with stub drawing magenta\n."
+        "               This allows for profiling to separate fragment-shader time.\n";
 }
 
 
@@ -319,6 +321,8 @@ int main(int argc, char **argv)
             retrace::debug = false;
             retrace::profiling = true;
             retrace::verbosity = -1;
+        } else if (!strcmp(arg, "--stub-fs")) {
+            retrace::stubFragmentShaders = true;
         } else if (!strcmp(arg, "-c")) {
             comparePrefix = argv[++i];
             if (compareFrequency.empty()) {
-- 
1.7.10

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