The emscripten library call for glShaderSource() will insert #extension GL_OES_standard_derivatives : enable if it detects dFdx, dFdy, or fwidth in the source. Unfortunately, that makes shaders that start with #version crash with the following error:
ERROR: 0:2: 'version' : #version directive must occur before anything else, except for comments and white space
This error is especially confusing because the source did start with #version.
| <!DOCTYPE html> | |
| <html> | |
| <head> | |
| <meta charset="utf-8"> | |
| </head> | |
| <body> | |
| <script> | |
| Module = this.Module || {}; | |
| Module.ctx = document.createElement('canvas').getContext('experimental-webgl'); | |
| </script> | |
| <script src="a.out.js"></script> | |
| </body> | |
| </html> |
| #include <GLES2/gl2.h> | |
| #include <stdio.h> | |
| int main() { | |
| const char *source = | |
| "#version 100\n" | |
| "void main() {\n" | |
| " gl_FragColor = vec4(dFdx(gl_FragCoord.x));\n" | |
| "}\n"; | |
| int shader = glCreateShader(GL_FRAGMENT_SHADER); | |
| glShaderSource(shader, 1, &source, NULL); | |
| glCompileShader(shader); | |
| int compileStatus = 0; | |
| glGetShaderiv(shader, GL_COMPILE_STATUS, &compileStatus); | |
| int length = 0; | |
| glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &length); | |
| char data[length]; | |
| glGetShaderInfoLog(shader, length, NULL, data); | |
| puts(data); | |
| return 0; | |
| } |
| SDK = ~/.emsdk_portable | |
| EMSCRIPTEN_PATH = $(shell $(SDK)/emsdk active_path emscripten-1.7.8) | |
| CLANG_PATH = $(shell dirname $(shell PATH=$(shell $(SDK)/emsdk active_path clang-3.2-64bit):$(PATH) which clang)) | |
| EMCC = LLVM=$(CLANG_PATH) python $(shell PATH=$(EMSCRIPTEN_PATH):$(PATH) which emcc) | |
| default: build | |
| build: | |
| $(EMCC) main.cpp |