Examples; imgui_impl_opengl3.cpp to work with Emscripten (#1941)

* Add some ifdefs to add emscripten specific params and includes

* Update imgui_impl_opengl3.cpp

* Update imgui_impl_opengl3.cpp

* Update imgui_impl_opengl3.cpp

* replace __EMSCRIPTEN_BUILD__ with __EMSCRIPTEN__

* replace GLFW_INCLUDE_ES3 with direct header

* removing useless glfw include

* Making call to glPolygonMode() optional

examples/imgui_impl_opengl3.cpp

@@ -37,7 +37,7 @@
 //  3.2       150       "#version 150"
 //  3.3       330
 //  4.0       400
-//  4.1       410
+//  4.1       410       "#version 410 core"
 //  4.2       420
 //  4.3       430
 //  ES 2.0    100       "#version 100"
@@ -57,7 +57,11 @@
 #include <stdint.h>     // intptr_t
 #endif
 
-#include <GL/gl3w.h>    // This example is using gl3w to access OpenGL functions. You may use another OpenGL loader/header such as: glew, glext, glad, glLoadGen, etc.
+#ifdef __EMSCRIPTEN__
+    #include <GLES3/gl3.h>
+#else
+    #include <GL/gl3w.h>    // This example is using gl3w to access OpenGL functions. You may use another OpenGL loader/header such as: glew, glext, glad, glLoadGen, etc.
+#endif
 //#include <glew.h>
 //#include <glext.h>
 //#include <glad/glad.h>
@@ -114,7 +118,9 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
     GLint last_sampler; glGetIntegerv(GL_SAMPLER_BINDING, &last_sampler);
     GLint last_array_buffer; glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &last_array_buffer);
     GLint last_vertex_array; glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &last_vertex_array);
-    GLint last_polygon_mode[2]; glGetIntegerv(GL_POLYGON_MODE, last_polygon_mode);
+    #ifdef GL_POLYGON_MODE
+        GLint last_polygon_mode[2]; glGetIntegerv(GL_POLYGON_MODE, last_polygon_mode);
+    #endif
     GLint last_viewport[4]; glGetIntegerv(GL_VIEWPORT, last_viewport);
     GLint last_scissor_box[4]; glGetIntegerv(GL_SCISSOR_BOX, last_scissor_box);
     GLenum last_blend_src_rgb; glGetIntegerv(GL_BLEND_SRC_RGB, (GLint*)&last_blend_src_rgb);
@@ -135,7 +141,9 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
     glDisable(GL_CULL_FACE);
     glDisable(GL_DEPTH_TEST);
     glEnable(GL_SCISSOR_TEST);
-    glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
+    #ifdef glPolygonMode
+        glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
+    #endif
 
     // Setup viewport, orthographic projection matrix
     // Our visible imgui space lies from draw_data->DisplayPps (top left) to draw_data->DisplayPos+data_data->DisplaySize (bottom right). DisplayMin is typically (0,0) for single viewport apps.
@@ -221,7 +229,9 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
     if (last_enable_cull_face) glEnable(GL_CULL_FACE); else glDisable(GL_CULL_FACE);
     if (last_enable_depth_test) glEnable(GL_DEPTH_TEST); else glDisable(GL_DEPTH_TEST);
     if (last_enable_scissor_test) glEnable(GL_SCISSOR_TEST); else glDisable(GL_SCISSOR_TEST);
-    glPolygonMode(GL_FRONT_AND_BACK, (GLenum)last_polygon_mode[0]);
+    #ifdef glPolygonMode
+        glPolygonMode(GL_FRONT_AND_BACK, (GLenum)last_polygon_mode[0]);
+    #endif
     glViewport(last_viewport[0], last_viewport[1], (GLsizei)last_viewport[2], (GLsizei)last_viewport[3]);
     glScissor(last_scissor_box[0], last_scissor_box[1], (GLsizei)last_scissor_box[2], (GLsizei)last_scissor_box[3]);
 }
@@ -340,6 +350,35 @@ bool    ImGui_ImplOpenGL3_CreateDeviceObjects()
         "    gl_Position = ProjMtx * vec4(Position.xy,0,1);\n"
         "}\n";
 
+    const GLchar* vertex_shader_glsl_300_es =
+        "precision mediump float;\n"
+        "layout (location = 0) in vec2 Position;\n"
+        "layout (location = 1) in vec2 UV;\n"
+        "layout (location = 2) in vec4 Color;\n"
+        "uniform mat4 ProjMtx;\n"
+        "out vec2 Frag_UV;\n"
+        "out vec4 Frag_Color;\n"
+        "void main()\n"
+        "{\n"
+        "    Frag_UV = UV;\n"
+        "    Frag_Color = Color;\n"
+        "    gl_Position = ProjMtx * vec4(Position.xy,0,1);\n"
+        "}\n";
+
+    const GLchar* vertex_shader_glsl_410_core =
+        "layout (location = 0) in vec2 Position;\n"
+        "layout (location = 1) in vec2 UV;\n"
+        "layout (location = 2) in vec4 Color;\n"
+        "uniform mat4 ProjMtx;\n"
+        "out vec2 Frag_UV;\n"
+        "out vec4 Frag_Color;\n"
+        "void main()\n"
+        "{\n"
+        "    Frag_UV = UV;\n"
+        "    Frag_Color = Color;\n"
+        "    gl_Position = ProjMtx * vec4(Position.xy,0,1);\n"
+        "}\n";
+
     const GLchar* fragment_shader_glsl_120 =
         "#ifdef GL_ES\n"
         "    precision mediump float;\n"
@@ -362,10 +401,41 @@ bool    ImGui_ImplOpenGL3_CreateDeviceObjects()
         "    Out_Color = Frag_Color * texture(Texture, Frag_UV.st);\n"
         "}\n";
 
+    const GLchar* fragment_shader_glsl_300_es =
+        "precision mediump float;\n"
+        "uniform sampler2D Texture;\n"
+        "in vec2 Frag_UV;\n"
+        "in vec4 Frag_Color;\n"
+        "layout (location = 0) out vec4 Out_Color;\n"
+        "void main()\n"
+        "{\n"
+        "    Out_Color = Frag_Color * texture(Texture, Frag_UV.st);\n"
+        "}\n";
+
+    const GLchar* fragment_shader_glsl_410_core =
+        "in vec2 Frag_UV;\n"
+        "in vec4 Frag_Color;\n"
+        "uniform sampler2D Texture;\n"
+        "layout (location = 0) out vec4 Out_Color;\n"
+        "void main()\n"
+        "{\n"
+        "    Out_Color = Frag_Color * texture(Texture, Frag_UV.st);\n"
+        "}\n";
+
     // Select shaders matching our GLSL versions
     const GLchar* vertex_shader = NULL;
     const GLchar* fragment_shader = NULL;
-    if (glsl_version < 130)
+    if(glsl_version == 410)
+    {
+        vertex_shader = vertex_shader_glsl_410_core;
+        fragment_shader = fragment_shader_glsl_410_core;
+    }
+    else if(glsl_version == 300)
+    {
+        vertex_shader = vertex_shader_glsl_300_es;
+        fragment_shader = fragment_shader_glsl_300_es;
+    }
+    else if (glsl_version < 130)
     {
         vertex_shader = vertex_shader_glsl_120;
         fragment_shader = fragment_shader_glsl_120;