OpenGLHostDisplay: Add a GLES2 render path

src/frontend-common/imgui_impl_opengl3.cpp

@@ -90,6 +90,7 @@ static int          g_AttribLocationTex = 0, g_AttribLocationProjMtx = 0;
 static int          g_AttribLocationVtxPos = 0, g_AttribLocationVtxUV = 0, g_AttribLocationVtxColor = 0; // Vertex attributes location
 static unsigned int g_VboHandle = 0, g_VaoHandle = 0, g_ElementsHandle = 0;
 static bool         g_IsGLES = false;
+static bool         g_IsGLES2 = false;
 
 // Forward Declarations
 static void ImGui_ImplOpenGL3_InitPlatformInterface();
@@ -104,23 +105,26 @@ bool    ImGui_ImplOpenGL3_Init(const char* glsl_version)
     io.BackendFlags |= ImGuiBackendFlags_RendererHasViewports;  // We can create multi-viewports on the Renderer side (optional)
 
     // Store GLSL version string so we can refer to it later in case we recreate shaders. Note: GLSL version is NOT the same as GL version. Leave this to NULL if unsure.
-    if (GLAD_GL_ES_VERSION_2_0)
+    if (GLAD_GL_ES_VERSION_3_0)
-    {
-      if (glsl_version == NULL)
-        glsl_version = "#version 100";
-      g_IsGLES = true;
-    }
-    else if (GLAD_GL_ES_VERSION_3_0)
     {
       if (glsl_version == NULL)
         glsl_version = "#version 300 es";
       g_IsGLES = true;
+      g_IsGLES2 = false;
+    }
+    else if (GLAD_GL_ES_VERSION_2_0)
+    {
+      if (glsl_version == NULL)
+        glsl_version = "#version 100";
+      g_IsGLES = true;
+      g_IsGLES2 = true;
     }
     else
     {
       if (glsl_version == NULL)
         glsl_version = "#version 130";
       g_IsGLES = false;
+      g_IsGLES2 = false;
     }
 
     if (!g_IsGLES)
@@ -179,11 +183,24 @@ static void ImGui_ImplOpenGL3_SetupRenderState(ImDrawData* draw_data, int fb_wid
     glUseProgram(g_ShaderHandle);
     glUniform1i(g_AttribLocationTex, 0);
     glUniformMatrix4fv(g_AttribLocationProjMtx, 1, GL_FALSE, &ortho_projection[0][0]);
-#ifndef IMGUI_IMPL_OPENGL_ES2
-    glBindSampler(0, 0); // We use combined texture/sampler state. Applications using GL 3.3 may set that otherwise.
-#endif
 
+    if (!g_IsGLES2)
+    {
         glBindVertexArray(g_VaoHandle);
+    }
+    else
+    {
+        glEnableVertexAttribArray(g_AttribLocationVtxPos);
+        glEnableVertexAttribArray(g_AttribLocationVtxUV);
+        glEnableVertexAttribArray(g_AttribLocationVtxColor);
+        glVertexAttribPointer(g_AttribLocationVtxPos, 2, GL_FLOAT, GL_FALSE, sizeof(ImDrawVert),
+            (GLvoid*)IM_OFFSETOF(ImDrawVert, pos));
+        glVertexAttribPointer(g_AttribLocationVtxUV, 2, GL_FLOAT, GL_FALSE, sizeof(ImDrawVert),
+            (GLvoid*)IM_OFFSETOF(ImDrawVert, uv));
+        glVertexAttribPointer(g_AttribLocationVtxColor, 4, GL_UNSIGNED_BYTE, GL_TRUE, sizeof(ImDrawVert),
+            (GLvoid*)IM_OFFSETOF(ImDrawVert, col));
+    }
+
     glBindBuffer(GL_ARRAY_BUFFER, g_VboHandle);
     glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, g_ElementsHandle);
 }
@@ -250,6 +267,19 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
             }
         }
     }
+
+    if (!g_IsGLES2)
+    {
+        glBindVertexArray(0);
+        glBindBuffer(GL_ARRAY_BUFFER, 0);
+        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
+    }
+    else
+    {
+        glDisableVertexAttribArray(g_AttribLocationVtxPos);
+        glDisableVertexAttribArray(g_AttribLocationVtxUV);
+        glDisableVertexAttribArray(g_AttribLocationVtxColor);
+    }
 }
 
 bool ImGui_ImplOpenGL3_CreateFontsTexture()
@@ -499,6 +529,9 @@ bool    ImGui_ImplOpenGL3_CreateDeviceObjects()
     glBindBuffer(GL_ARRAY_BUFFER, g_VboHandle);
     glBufferData(GL_ARRAY_BUFFER, sizeof(ImDrawVert), nullptr, GL_STREAM_DRAW);
 
+
+    if (!g_IsGLES2)
+    {
         glGenVertexArrays(1, &g_VaoHandle);
         glBindVertexArray(g_VaoHandle);
 
@@ -511,15 +544,15 @@ bool    ImGui_ImplOpenGL3_CreateDeviceObjects()
                               (GLvoid*)IM_OFFSETOF(ImDrawVert, uv));
         glVertexAttribPointer(g_AttribLocationVtxColor, 4, GL_UNSIGNED_BYTE, GL_TRUE, sizeof(ImDrawVert),
                               (GLvoid*)IM_OFFSETOF(ImDrawVert, col));
+    }
 
     ImGui_ImplOpenGL3_CreateFontsTexture();
 
     // Restore modified GL state
     glBindTexture(GL_TEXTURE_2D, last_texture);
     glBindBuffer(GL_ARRAY_BUFFER, last_array_buffer);
-#ifndef IMGUI_IMPL_OPENGL_ES2
+    if (!g_IsGLES2)
         glBindVertexArray(last_vertex_array);
-#endif
 
     return true;
 }

src/frontend-common/opengl_host_display.cpp

@@ -466,6 +466,9 @@ void OpenGLHostDisplay::DestroyImGuiContext()
 
 bool OpenGLHostDisplay::CreateResources()
 {
+  m_use_gles2_draw_path = m_gl_context->IsGLES() && !GLAD_GL_ES_VERSION_3_0;
+  if (!m_use_gles2_draw_path)
+  {
     static constexpr char fullscreen_quad_vertex_shader[] = R"(
 uniform vec4 u_src_rect;
 out vec2 v_tex0;
@@ -541,6 +544,74 @@ void main()
     glGenSamplers(1, &m_display_linear_sampler);
     glSamplerParameteri(m_display_linear_sampler, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
     glSamplerParameteri(m_display_linear_sampler, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+  }
+  else
+  {
+    static constexpr char fullscreen_quad_vertex_shader[] = R"(
+#version 100
+
+attribute highp vec2 a_pos;
+attribute highp vec2 a_tex0;
+varying highp vec2 v_tex0;
+
+void main()
+{
+  gl_Position = vec4(a_pos, 0.0, 1.0);
+  v_tex0 = a_tex0;
+}
+)";
+
+    static constexpr char display_fragment_shader[] = R"(
+#version 100
+
+uniform highp sampler2D samp0;
+
+varying highp vec2 v_tex0;
+
+void main()
+{
+  gl_FragColor = vec4(texture2D(samp0, v_tex0).rgb, 1.0);
+}
+)";
+
+    static constexpr char cursor_fragment_shader[] = R"(
+#version 100
+
+uniform highp sampler2D samp0;
+
+varying highp vec2 v_tex0;
+
+void main()
+{
+  gl_FragColor = texture2D(samp0, v_tex0);
+}
+)";
+
+    if (!m_display_program.Compile(fullscreen_quad_vertex_shader, {}, display_fragment_shader) ||
+        !m_cursor_program.Compile(fullscreen_quad_vertex_shader, {}, cursor_fragment_shader))
+    {
+      Log_ErrorPrintf("Failed to compile display shaders");
+      return false;
+    }
+
+    m_display_program.BindAttribute(0, "a_pos");
+    m_display_program.BindAttribute(1, "a_tex0");
+    m_cursor_program.BindAttribute(0, "a_pos");
+    m_cursor_program.BindAttribute(1, "a_tex0");
+
+    if (!m_display_program.Link() || !m_cursor_program.Link())
+    {
+      Log_ErrorPrintf("Failed to link display programs");
+      return false;
+    }
+
+    m_display_program.Bind();
+    m_display_program.RegisterUniform("samp0");
+    m_display_program.Uniform1i(0, 0);
+    m_cursor_program.Bind();
+    m_cursor_program.RegisterUniform("samp0");
+    m_cursor_program.Uniform1i(0, 0);
+  }
 
   return true;
 }
@@ -561,11 +632,20 @@ void OpenGLHostDisplay::DestroyResources()
   }
 
   if (m_display_vao != 0)
+  {
     glDeleteVertexArrays(1, &m_display_vao);
+    m_display_vao = 0;
+  }
   if (m_display_linear_sampler != 0)
+  {
     glDeleteSamplers(1, &m_display_linear_sampler);
+    m_display_linear_sampler = 0;
+  }
   if (m_display_nearest_sampler != 0)
+  {
     glDeleteSamplers(1, &m_display_nearest_sampler);
+    m_display_nearest_sampler = 0;
+  }
 
   m_cursor_program.Destroy();
   m_display_program.Destroy();
@@ -641,6 +721,30 @@ void OpenGLHostDisplay::RenderDisplay()
                 m_display_texture_view_width, m_display_texture_view_height, m_display_linear_filtering);
 }
 
+static void DrawFullscreenQuadES2(s32 tex_view_x, s32 tex_view_y, s32 tex_view_width, s32 tex_view_height,
+                                  s32 tex_width, s32 tex_height)
+{
+  const float tex_left = static_cast<float>(tex_view_x) / static_cast<float>(tex_width);
+  const float tex_right = tex_left + static_cast<float>(tex_view_width) / static_cast<float>(tex_width);
+  const float tex_top = static_cast<float>(tex_view_y) / static_cast<float>(tex_height);
+  const float tex_bottom = tex_top + static_cast<float>(tex_view_height) / static_cast<float>(tex_height);
+  const std::array<std::array<float, 4>, 4> vertices = {{
+    {{-1.0f, -1.0f, tex_left, tex_bottom}}, // bottom-left
+    {{1.0f, -1.0f, tex_right, tex_bottom}}, // bottom-right
+    {{-1.0f, 1.0f, tex_left, tex_top}},     // top-left
+    {{1.0f, 1.0f, tex_right, tex_top}},     // top-right
+  }};
+
+  glBindBuffer(GL_ARRAY_BUFFER, 0);
+  glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(vertices[0]), &vertices[0][0]);
+  glEnableVertexAttribArray(0);
+  glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, sizeof(vertices[0]), &vertices[0][2]);
+  glEnableVertexAttribArray(1);
+  glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+  glDisableVertexAttribArray(1);
+  glDisableVertexAttribArray(0);
+}
+
 void OpenGLHostDisplay::RenderDisplay(s32 left, s32 bottom, s32 width, s32 height, void* texture_handle,
                                       u32 texture_width, s32 texture_height, s32 texture_view_x, s32 texture_view_y,
                                       s32 texture_view_width, s32 texture_view_height, bool linear_filter)
@@ -651,16 +755,25 @@ void OpenGLHostDisplay::RenderDisplay(s32 left, s32 bottom, s32 width, s32 heigh
   glDisable(GL_DEPTH_TEST);
   glDisable(GL_SCISSOR_TEST);
   glDepthMask(GL_FALSE);
+  glBindTexture(GL_TEXTURE_2D, static_cast<GLuint>(reinterpret_cast<uintptr_t>(texture_handle)));
   m_display_program.Bind();
+
+  if (!m_use_gles2_draw_path)
+  {
     m_display_program.Uniform4f(0, static_cast<float>(texture_view_x) / static_cast<float>(texture_width),
                                 static_cast<float>(texture_view_y) / static_cast<float>(texture_height),
                                 (static_cast<float>(texture_view_width) - 0.5f) / static_cast<float>(texture_width),
                                 (static_cast<float>(texture_view_height) + 0.5f) / static_cast<float>(texture_height));
-  glBindTexture(GL_TEXTURE_2D, static_cast<GLuint>(reinterpret_cast<uintptr_t>(texture_handle)));
     glBindSampler(0, linear_filter ? m_display_linear_sampler : m_display_nearest_sampler);
     glBindVertexArray(m_display_vao);
     glDrawArrays(GL_TRIANGLES, 0, 3);
     glBindSampler(0, 0);
+  }
+  else
+  {
+    DrawFullscreenQuadES2(m_display_texture_view_x, m_display_texture_view_y, m_display_texture_view_width,
+                          m_display_texture_view_height, m_display_texture_width, m_display_texture_height);
+  }
 }
 
 void OpenGLHostDisplay::RenderSoftwareCursor()
@@ -684,12 +797,22 @@ void OpenGLHostDisplay::RenderSoftwareCursor(s32 left, s32 bottom, s32 width, s3
   glDisable(GL_SCISSOR_TEST);
   glDepthMask(GL_FALSE);
   m_cursor_program.Bind();
-  m_cursor_program.Uniform4f(0, 0.0f, 0.0f, 1.0f, 1.0f);
   glBindTexture(GL_TEXTURE_2D, static_cast<OpenGLHostDisplayTexture*>(texture_handle)->GetGLID());
+
+  if (!m_use_gles2_draw_path)
+  {
+    m_cursor_program.Uniform4f(0, 0.0f, 0.0f, 1.0f, 1.0f);
     glBindSampler(0, m_display_linear_sampler);
     glBindVertexArray(m_display_vao);
     glDrawArrays(GL_TRIANGLES, 0, 3);
     glBindSampler(0, 0);
+  }
+  else
+  {
+    const s32 tex_width = static_cast<s32>(static_cast<OpenGLHostDisplayTexture*>(texture_handle)->GetWidth());
+    const s32 tex_height = static_cast<s32>(static_cast<OpenGLHostDisplayTexture*>(texture_handle)->GetHeight());
+    DrawFullscreenQuadES2(0, 0, tex_width, tex_height, tex_width, tex_height);
+  }
 }
 
 #ifndef LIBRETRO

src/frontend-common/opengl_host_display.h

@@ -120,6 +120,8 @@ protected:
   std::unique_ptr<GL::StreamBuffer> m_post_processing_ubo;
   std::vector<PostProcessingStage> m_post_processing_stages;
 #endif
+
+  bool m_use_gles2_draw_path = false;
 };
 
 } // namespace FrontendCommon