preparing for drawing points as instances

wkjarosz · Dec 26, 2023 · 7e71ba6 · 7e71ba6
1 parent ecb142e
commit 7e71ba6
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Showing 3 changed files with 47 additions and 24 deletions.
diff --git a/assets/shaders/points.frag b/assets/shaders/points.frag
@@ -3,7 +3,7 @@ uniform float point_size;
 void          main()
 {
     float alpha = 1.0;
-    if (point_size > 3.0)
+    // if (point_size > 3.0)
     {
         vec2  circCoord = 2.0 * gl_PointCoord - 1.0;
         float radius2   = dot(circCoord, circCoord);

diff --git a/include/shader.h b/include/shader.h
@@ -128,24 +128,21 @@ class Shader
     template <typename T>
     void set_uniform(const std::string &name, const T &value)
     {
-        size_t       shape[3] = {1, 1, 1};
-        size_t       ndim     = (size_t)-1;
-        const void  *data;
-        VariableType vtype = VariableType::Invalid;
-
+        size_t shape[3] = {1, 1, 1};
         if constexpr (std::is_scalar_v<T>)
-        {
-            data  = &value;
-            ndim  = 0;
-            vtype = get_type<T>();
-        }
-
-        if (ndim == (size_t)-1)
+            set_buffer(name, get_type<T>(), 0, shape, &value);
+        else
             throw std::runtime_error("Shader::set_uniform(): invalid input array dimension!");
-
-        set_buffer(name, vtype, ndim, shape, data);
     }
 
+    /**
+        Set the "rate at which generic vertex attributes advance when rendering multiple instances"
+        see:
+            https://registry.khronos.org/OpenGL-Refpages/es3/html/glVertexAttribDivisor.xhtml
+            https://registry.khronos.org/OpenGL-Refpages/gl4/html/glVertexAttribDivisor.xhtml
+    */
+    void set_buffer_divisor(const std::string &name, size_t divisor);
+
     // /**
     //  * \brief Associate a texture with a named shader parameter
     //  *
@@ -185,8 +182,13 @@ class Shader
         \param indexed
             Render indexed geometry? In this case, an \c uint32_t valued buffer with name \c indices must have been
             uploaded using \ref set().
+
+        \param instances
+            If you want to render instances, set this to > 0. In this case, make sure to call \ref set_buffer_divisor()
+       for each registered buffer beforehand to inform the shader how the instances should access the buffers.
     */
-    void draw_array(PrimitiveType primitive_type, size_t offset, size_t count, bool indexed = false);
+    void draw_array(PrimitiveType primitive_type, size_t offset, size_t count, bool indexed = false,
+                    size_t instances = 0u);
 
 #if defined(HELLOIMGUI_HAS_OPENGL)
     uint32_t shader_handle() const
@@ -229,8 +231,9 @@ class Shader
         int          index  = 0;
         size_t       ndim   = 0;
         size_t       shape[3]{0, 0, 0};
-        size_t       size  = 0;
-        bool         dirty = false;
+        size_t       size             = 0;
+        size_t       instance_divisor = 0;
+        bool         dirty            = false;
 
         std::string to_string() const;
     };

diff --git a/src/shader.cpp b/src/shader.cpp
@@ -8,8 +8,6 @@
 
 #include <fmt/core.h>
 
-#include <iostream>
-
 using std::string;
 
 bool check_glerror(const char *cmd)
@@ -382,6 +380,16 @@ void Shader::set_buffer(const std::string &name, VariableType dtype, size_t ndim
     buf.dirty = true;
 }
 
+void Shader::set_buffer_divisor(const std::string &name, size_t divisor)
+{
+    auto it = m_buffers.find(name);
+    if (it == m_buffers.end())
+        throw std::runtime_error("Shader::set_buffer(): could not find argument named \"" + name + "\"");
+
+    Buffer &buf          = m_buffers[name];
+    buf.instance_divisor = divisor;
+}
+
 // void Shader::set_texture(const std::string &name, Texture *texture)
 // {
 //     auto it = m_buffers.find(name);
@@ -454,6 +462,7 @@ void Shader::begin()
                                          std::to_string(buf.ndim) + ")");
 
             CHK(glVertexAttribPointer(buf.index, (GLint)buf.shape[1], gl_type, GL_FALSE, 0, nullptr));
+            CHK(glVertexAttribDivisor(buf.index, (GLuint)buf.instance_divisor));
             break;
 
         case VertexTexture:
@@ -617,7 +626,7 @@ void Shader::end()
     CHK(glUseProgram(0));
 }
 
-void Shader::draw_array(PrimitiveType primitive_type, size_t offset, size_t count, bool indexed)
+void Shader::draw_array(PrimitiveType primitive_type, size_t offset, size_t count, bool indexed, size_t instances)
 {
     GLenum primitive_type_gl;
     switch (primitive_type)
@@ -633,10 +642,21 @@ void Shader::draw_array(PrimitiveType primitive_type, size_t offset, size_t coun
     }
 
     if (!indexed)
-        CHK(glDrawArrays(primitive_type_gl, (GLint)offset, (GLsizei)count));
+    {
+        if (instances == 0)
+            CHK(glDrawArrays(primitive_type_gl, (GLint)offset, (GLsizei)count));
+        else
+            CHK(glDrawArraysInstanced(primitive_type_gl, (GLint)offset, (GLsizei)count, instances));
+    }
     else
-        CHK(glDrawElements(primitive_type_gl, (GLsizei)count, GL_UNSIGNED_INT,
-                           (const void *)(offset * sizeof(uint32_t))));
+    {
+        if (instances == 0)
+            CHK(glDrawElements(primitive_type_gl, (GLsizei)count, GL_UNSIGNED_INT,
+                               (const void *)(offset * sizeof(uint32_t))));
+        else
+            CHK(glDrawElementsInstanced(primitive_type_gl, (GLsizei)count, GL_UNSIGNED_INT,
+                                        (const void *)(offset * sizeof(uint32_t)), instances));
+    }
 }
 
 std::string Shader::Buffer::to_string() const