1) Shader manager: Allow to override #defines programatically

when loading a shader file.
2) Conditional compilation of environmental mapping in gouraud.fs
   using 1)

resources/shaders/gouraud.fs

@@ -16,8 +16,10 @@ struct SlopeDetection
 uniform vec4 uniform_color;
 uniform SlopeDetection slope;
 
-uniform sampler2D environment_tex;
-uniform bool use_environment_tex;
+#if ENABLE_ENVIRONMENT_MAP
+    uniform sampler2D environment_tex;
+    uniform bool use_environment_tex;
+#endif // ENABLE_ENVIRONMENT_MAP
 
 varying vec3 clipping_planes_dots;
 
@@ -42,8 +44,10 @@ void main()
 	vec3 color = slope.actived ? slope_color() : uniform_color.rgb;
     // if the fragment is outside the print volume -> use darker color
 	color = (any(lessThan(delta_box_min, ZERO)) || any(greaterThan(delta_box_max, ZERO))) ? mix(color, ZERO, 0.3333) : color;
+#if ENABLE_ENVIRONMENT_MAP
     if (use_environment_tex)
         gl_FragColor = vec4(0.45 * texture2D(environment_tex, normalize(eye_normal).xy * 0.5 + 0.5).xyz + 0.8 * color * intensity.x, uniform_color.a);
     else
+#endif
         gl_FragColor = vec4(vec3(intensity.y) + color * intensity.x, uniform_color.a);
 }

src/slic3r/GUI/3DScene.hpp

@@ -611,7 +611,7 @@ struct _3DScene
     static void point3_to_verts(const Vec3crd& point, double width, double height, GLVolume& volume);
 };
 
-static constexpr float BedEpsilon = EPSILON;
+static constexpr float BedEpsilon = float(EPSILON);
 
 }
 

src/slic3r/GUI/GLShader.cpp

@@ -18,9 +18,10 @@ GLShaderProgram::~GLShaderProgram()
         glsafe(::glDeleteProgram(m_id));
 }
 
-bool GLShaderProgram::init_from_files(const std::string& name, const ShaderFilenames& filenames)
+bool GLShaderProgram::init_from_files(const std::string& name, const ShaderFilenames& filenames, const std::initializer_list<std::string_view> &defines)
 {
-    auto load_from_file = [](const std::string& filename) {
+    // Load a shader program from file, prepend defs block.
+    auto load_from_file = [](const std::string& filename, const std::string &defs) {
         std::string path = resources_dir() + "/shaders/" + filename;
         boost::nowide::ifstream s(path, boost::nowide::ifstream::binary);
         if (!s.good()) {
@@ -31,20 +32,39 @@ bool GLShaderProgram::init_from_files(const std::string& name, const ShaderFilen
         s.seekg(0, s.end);
         int file_length = static_cast<int>(s.tellg());
         s.seekg(0, s.beg);
-        std::string source(file_length, '\0');
-        s.read(source.data(), file_length);
+        std::string source(defs.size() + file_length, '\0');
+        memcpy(source.data(), defs.c_str(), defs.size());
+        s.read(source.data() + defs.size(), file_length);
         if (!s.good()) {
             BOOST_LOG_TRIVIAL(error) << "Error while loading file: '" << path << "'";
             return std::string();
         }
-
         s.close();
+
+        if (! defs.empty()) {
+            // Extract the version and flip the order of "defines" and version in the source block.
+            size_t idx = source.find("\n", defs.size());
+            if (idx != std::string::npos && strncmp(source.c_str() + defs.size(), "#version", 8) == 0) {
+                // Swap the version line with the defines.
+                size_t len = idx - defs.size() + 1;
+                memmove(source.data(), source.c_str() + defs.size(), len);
+                memcpy(source.data() + len, defs.c_str(), defs.size());
+            }
+        }
+
         return source;
     };
 
+    // Create a block of C "defines" from list of symbols.
+    std::string defines_program;
+    for (std::string_view def : defines)
+        // Our shaders are stored with "\r\n", thus replicate the same here for consistency. Likely "\n" would suffice, 
+        // but we don't know all the OpenGL shader compilers around.
+        defines_program += format("#define %s 1\r\n", def);
+
     ShaderSources sources = {};
     for (size_t i = 0; i < static_cast<size_t>(EShaderType::Count); ++i) {
-        sources[i] = filenames[i].empty() ? std::string() : load_from_file(filenames[i]);
+        sources[i] = filenames[i].empty() ? std::string() : load_from_file(filenames[i], defines_program);
     }
 
     bool valid = !sources[static_cast<size_t>(EShaderType::Vertex)].empty() && !sources[static_cast<size_t>(EShaderType::Fragment)].empty() && sources[static_cast<size_t>(EShaderType::Compute)].empty();

src/slic3r/GUI/GLShader.hpp

@@ -3,6 +3,7 @@
 
 #include <array>
 #include <string>
+#include <string_view>
 
 #include "libslic3r/Point.hpp"
 
@@ -32,7 +33,7 @@ private:
 public:
     ~GLShaderProgram();
 
-    bool init_from_files(const std::string& name, const ShaderFilenames& filenames);
+    bool init_from_files(const std::string& name, const ShaderFilenames& filenames, const std::initializer_list<std::string_view> &defines = {});
     bool init_from_texts(const std::string& name, const ShaderSources& sources);
 
     const std::string& get_name() const { return m_name; }

src/slic3r/GUI/GLShadersManager.cpp

@@ -5,6 +5,8 @@
 
 #include <cassert>
 #include <algorithm>
+#include <string_view>
+using namespace std::literals;
 
 #include <GL/glew.h>
 
@@ -14,9 +16,10 @@ std::pair<bool, std::string> GLShadersManager::init()
 {
     std::string error;
 
-    auto append_shader = [this, &error](const std::string& name, const GLShaderProgram::ShaderFilenames& filenames) {
+    auto append_shader = [this, &error](const std::string& name, const GLShaderProgram::ShaderFilenames& filenames, 
+        const std::initializer_list<std::string_view> &defines = {}) {
         m_shaders.push_back(std::make_unique<GLShaderProgram>());
-        if (!m_shaders.back()->init_from_files(name, filenames)) {
+        if (!m_shaders.back()->init_from_files(name, filenames, defines)) {
             error += name + "\n";
             // if any error happens while initializating the shader, we remove it from the list
             m_shaders.pop_back();
@@ -40,7 +43,11 @@ std::pair<bool, std::string> GLShadersManager::init()
     // used to render extrusion and travel paths as lines in gcode preview
     valid &= append_shader("toolpaths_lines", { "toolpaths_lines.vs", "toolpaths_lines.fs" });
     // used to render objects in 3d editor
-    valid &= append_shader("gouraud", { "gouraud.vs", "gouraud.fs" });
+    valid &= append_shader("gouraud", { "gouraud.vs", "gouraud.fs" }
+#if ENABLE_ENVIRONMENT_MAP
+        , { "ENABLE_ENVIRONMENT_MAP"sv }
+#endif
+        );
     // used to render variable layers heights in 3d editor
     valid &= append_shader("variable_layer_height", { "variable_layer_height.vs", "variable_layer_height.fs" });
 
@@ -49,14 +56,12 @@ std::pair<bool, std::string> GLShadersManager::init()
 
 void GLShadersManager::shutdown()
 {
-    for (std::unique_ptr<GLShaderProgram>& shader : m_shaders) {
-        shader.reset();
-    }
+    m_shaders.clear();
 }
 
 GLShaderProgram* GLShadersManager::get_shader(const std::string& shader_name)
 {
-    auto it = std::find_if(m_shaders.begin(), m_shaders.end(), [shader_name](std::unique_ptr<GLShaderProgram>& p) { return p->get_name() == shader_name; });
+    auto it = std::find_if(m_shaders.begin(), m_shaders.end(), [&shader_name](std::unique_ptr<GLShaderProgram>& p) { return p->get_name() == shader_name; });
     return (it != m_shaders.end()) ? it->get() : nullptr;
 }