glsl - Vertex and Fragment shaders for lighting effect in OpenGL ES20 -

i want add lighting effect in models via shaders. found out there vertex , fragment shaders make work on opengl:

static const char* vertsource = {     "uniform vec3 lightposition;\n"     "varying vec3 normal, eyevec, lightdir;\n"     "void main()\n"     "{\n"     "    vec4 vertexineye = gl_modelviewmatrix * gl_vertex;\n"     "    eyevec = -vertexineye.xyz;\n"     "    lightdir = vec3(lightposition - vertexineye.xyz);\n"     "    normal = gl_normalmatrix * gl_normal;\n"     "    gl_position = ftransform();\n"     "}\n" };  static const char* fragsource = {     "uniform vec4 lightdiffuse;\n"     "uniform vec4 lightspecular;\n"     "uniform float shininess;\n"     "varying vec3 normal, eyevec, lightdir;\n"     "void main (void)\n"     "{\n"     "  vec4 finalcolor = gl_frontlightmodelproduct.scenecolor;\n"     "  vec3 n = normalize(normal);\n"     "  vec3 l = normalize(lightdir);\n"     "  float lambert = dot(n,l);\n"     "  if (lambert > 0.0)\n"     "  {\n"     "    finalcolor += lightdiffuse * lambert;\n"     "    vec3 e = normalize(eyevec);\n"     "    vec3 r = reflect(-l, n);\n"     "    float specular = pow(max(dot(r, e), 0.0), shininess);\n"     "    finalcolor += lightspecular * specular;\n"     "  }\n"     "  gl_fragcolor = finalcolor;\n"     "}\n" }; 

the problem working in opengl es2, because developing android app. , seems in-built variable gl_frontlightmodelproduct not available gles20, because having compilation fails in line.

my question therefore is: how can modify above shaders make them work in opengl es20 context?

gl_frontlightmodelproduct.scenecolor gives ambient colour of scene can 0 if want area not affected light black. can replace vec4(0.0, 0.0, 0.0, 1.0);

you should remove these variables , send them uniforms.

1. gl_modelviewmatrix (send uniform)
2. gl_vertex (read attributes)
3. gl_normalmatrix (send uniform)
4. gl_normal (read attributes)

or instead of fighting in converting opengl shader, can search simple opengl es 2.0 shaders