Pretty print of shaders

src/gpu/gl/GrGLSLPrettyPrint.cpp

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#include "gl/GrGLSLPrettyPrint.h"
+
+namespace GrGLSLPrettyPrint {
+
+class GrGLSLPrettyPrint {

[bsalomon, 2014/08/04 15:20:01]

For classes that are private to a particular translation unit we don't usually
use the Gr prefix. That's also true for classes that are nested within another
Gr-prefixed class or Gr-prefixed namespace.

+public:
+    GrGLSLPrettyPrint() {}
+
+    SkString prettify(const SkString& input, bool countlines) {
+        // setup pretty state
+        fIndex = 0;
+        fLength = input.size();
+        fInput = input;
+        fCountlines = countlines;
+        fTabs = 0;
+        fLinecount = 1;
+        fFreshline = true;
+
+        int parensDepth = 0;
+        // number 1st line
+        lineNumbering();
+        while (fLength > fIndex) {
+            /* the heart and soul of our prettification algorithm.  The rules should hopefully be
+             * self explanatory.  For '#' and '//' tokens we parse until we reach a newline.
+             *
+             * For long style comments like this one, we search for the ending token.  We also
+             * preserve whitespace in these comments WITH THE CAVEAT that we do the newlines
+             * ourselves.  This allows us to remain in control of line numbers, and matching tabs
+             * Existing tabs in the input string are copied over too, but this will look funny
+             *
+             * '{' and '}' are handled in basically the same way.  We add a newline if we aren't
+             * on a fresh line, dirty the line, then add a second newline, ie braces are always
+             * on their own lines indented properly.  The one funkiness here is structs print with
+             * the semicolon on its own line.  Its not a problem for a glsl compiler though
+             *
+             * '(' and ')' are basically ignored, except as a sign we need to ignore ';' ala
+             * in for loops.
+             *
+             * ';' means add a new line
+             *
+             * '\t' and '\n' are ignored in general parsing for backwards compatability with
+             * existing shader code and we also have a special case for handling whitespace
+             * at the beginning of fresh lines.
+             *
+             * Otherwise just add the new character to the pretty string, indenting if necessary.
+             */
+            if (hasToken("#") || hasToken("//")) {

[Stephen White, 2014/08/04 15:10:29]

I guess ad hoc parsing is ok for this, since we know most of the time that the
input is conforming. If not, we might want to consider a real lexer.

OTOH, maybe we should just enforce the formatting in the shader generator
itself, and stop putting whitespace in the call sites at all. Just a thought.

[bsalomon, 2014/08/04 15:20:01]

Part of the advantage of having a separate function is that we don't worry about
it at all in a normal release run. The effects can optionally add whatever
whitespace they want, or not, and we just pass the ugly shader string down to
GL. We only pretty print in debug builds with shader dumping enabled or when a
shader failed to compile/link.

Because the Debug builds of our regression test tools will actually send the
pretty-printed string to GL we should catch any differences in language or
logical correctness introduced by the pretty printer.

+                parseUntilNewline();
+            } else if (hasToken("/*")) {

[bsalomon, 2014/08/04 15:20:01]

minor style nit: this->hasToken() (and similar in other places). We only do that
for methods, not data members.

+                parseUntil("*/");
+            } else if ('{' == fInput[fIndex]) {
+                newline();
+                appendChar('{');
+                fTabs++;
+                newline();
+            } else if ('}' == fInput[fIndex]) {
+                fTabs--;
+                newline();
+                appendChar('}');
+                newline();
+            } else if (hasToken(")")) {
+                parensDepth--;
+            } else if (hasToken("(")) {
+                parensDepth++;
+            } else if (!parensDepth && hasToken(";")) {
+                newline();
+            } else if ('\t' == fInput[fIndex] || '\n' == fInput[fIndex] ||
+                    (fFreshline && ' ' == fInput[fIndex])) {
+                fIndex++;
+                continue;
+            } else {
+                appendChar(input[fIndex]);
+            }
+        }
+        return fPretty;
+    }
+private:
+    void appendChar(char c) {
+        tabString();
+        fPretty.appendf("%c", fInput[fIndex++]);
+        fFreshline = false;
+    }
+
+    // hasToken automatically consumes the next token, if it is a match, and then tabs
+    // if necessary, before inserting the token into the pretty string
+    bool hasToken(const char* token) {
+        size_t i = fIndex;
+        for (size_t j = 0; token[j] && fLength > i; i++, j++) {
+            if (token[j] != fInput[i]) {
+                return false;
+            }
+        }
+        tabString();
+        fIndex = i;
+        fPretty.append(token);
+        fFreshline = false;
+        return true;
+    }
+
+    void parseUntilNewline() {
+        while (fLength > fIndex) {
+            if ('\n' == fInput[fIndex]) {
+                fIndex++;
+                newline();
+                break;
+            }
+            fPretty.appendf("%c", fInput[fIndex++]);
+        }
+    }
+
+    // this code assumes it is not actually searching for a newline.  If you need to search for a
+    // newline, then use the function above.  If you do search for a newline with this function
+    // it will consume the entire string and the output will certainly not be prettified
+    void parseUntil(const char* token) {
+        while (fLength > fIndex) {
+            // For embedded newlines,  this code will make sure to embed the newline in the
+            // pretty string, increase the linecount, and tab out the next line to the appropriate
+            // place
+            if ('\n' == fInput[fIndex]) {
+                newline();
+                tabString();
+                fIndex++;
+            }
+            if (hasToken(token)) {
+                break;
+            }
+            fFreshline = false;
+            fPretty.appendf("%c", fInput[fIndex++]);
+        }
+    }
+
+    // We only tab if on a newline, otherwise consider the line tabbed
+    void tabString() {
+        if (fFreshline) {
+            for (int t = 0; t < fTabs; t++) {
+                fPretty.append("\t");
+            }
+        }
+    }
+
+    // newline is really a request to add a newline, if we are on a fresh line there is no reason
+    // to add another newline
+    void newline() {
+        if (!fFreshline) {
+            fFreshline = true;
+            fPretty.append("\n");
+            lineNumbering();
+        }
+    }
+
+    void lineNumbering() {
+        if (fCountlines) {
+            fPretty.appendf("%4d\t", fLinecount++);
+        }
+    }
+
+    bool fCountlines, fFreshline, fRequestNewline;
+    int fTabs, fLinecount;
+    size_t fIndex, fLength;
+    SkString fInput, fPretty;
+};
+
+SkString PrettyPrintGLSL(const SkString& input, bool countlines) {
+    GrGLSLPrettyPrint pp;
+    return pp.prettify(input, countlines);
+}
+
+} // end namespace