feat(shaders_lab): scaffold C++ app with GLSL live-reload canvas

- cpp/functions/gfx: gl_shader, gl_framebuffer, fullscreen_quad, shader_canvas - cpp/apps/shaders_lab: main + 3 seed shaders (plasma, circle, checker) - ImGui docking layout: Code | Canvas | Controls Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
2026-04-24 20:32:14 +02:00
parent 5546ce6453
commit 042bb43b37
16 changed files with 823 additions and 0 deletions
@@ -0,0 +1,85 @@
+#define GL_GLEXT_PROTOTYPES
+#include <GL/gl.h>
+#include <GL/glext.h>
+
+#include "gfx/shader_canvas.h"
+#include "imgui.h"
+
+namespace fn::gfx {
+
+void canvas_init(ShaderCanvas& c) {
+    if (c.initialized) return;
+    fb_init(c.fb);
+    quad_init(c.quad);
+    c.initialized = true;
+}
+
+void canvas_set_program(ShaderCanvas& c, unsigned int program) {
+    if (c.program) delete_program(c.program);
+    c.program = program;
+}
+
+void canvas_render(ShaderCanvas& c, float time_seconds) {
+    ImVec2 avail = ImGui::GetContentRegionAvail();
+    int w = static_cast<int>(avail.x);
+    int h = static_cast<int>(avail.y);
+    if (w < 1) w = 1;
+    if (h < 1) h = 1;
+
+    fb_resize(c.fb, w, h);
+
+    // Save GL state
+    GLint prev_fbo = 0;
+    glGetIntegerv(GL_FRAMEBUFFER_BINDING, &prev_fbo);
+    GLint prev_vp[4];
+    glGetIntegerv(GL_VIEWPORT, prev_vp);
+
+    // Render to FBO
+    glBindFramebuffer(GL_FRAMEBUFFER, c.fb.fbo);
+    glViewport(0, 0, w, h);
+    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
+    glClear(GL_COLOR_BUFFER_BIT);
+
+    if (c.program) {
+        glUseProgram(c.program);
+
+        GLint loc_res = glGetUniformLocation(c.program, "u_resolution");
+        GLint loc_time = glGetUniformLocation(c.program, "u_time");
+        GLint loc_mouse = glGetUniformLocation(c.program, "u_mouse");
+
+        if (loc_res >= 0) glUniform2f(loc_res, static_cast<float>(w), static_cast<float>(h));
+        if (loc_time >= 0) glUniform1f(loc_time, time_seconds);
+        if (loc_mouse >= 0) {
+            ImVec2 mouse = ImGui::GetMousePos();
+            ImVec2 canvas_pos = ImGui::GetCursorScreenPos();
+            // cursor pos is AFTER content region starts
+            float mx = mouse.x - canvas_pos.x;
+            float my = static_cast<float>(h) - (mouse.y - canvas_pos.y);
+            glUniform2f(loc_mouse, mx, my);
+        }
+
+        quad_draw(c.quad);
+        glUseProgram(0);
+    }
+
+    // Restore GL state
+    glBindFramebuffer(GL_FRAMEBUFFER, static_cast<GLuint>(prev_fbo));
+    glViewport(prev_vp[0], prev_vp[1], prev_vp[2], prev_vp[3]);
+
+    // Draw texture in ImGui panel (flip V: OpenGL origin is bottom-left)
+    ImGui::Image(
+        (ImTextureID)(intptr_t)c.fb.tex,
+        avail,
+        ImVec2(0, 1), ImVec2(1, 0)
+    );
+}
+
+void canvas_destroy(ShaderCanvas& c) {
+    if (!c.initialized) return;
+    if (c.program) { delete_program(c.program); c.program = 0; }
+    quad_destroy(c.quad);
+    fb_destroy(c.fb);
+    c.initialized = false;
+}
+
+} // namespace fn::gfx