glVertexAttribPointer的怪異行爲

Question

我創建默認的VAO和一個VBO，並綁定它們。 我加載模型數據結構的陣列vertex_data_t

glBufferData(GL_ARRAY_BUFFER, nvertices * sizeof(vertex_data_t), vertices, GL_STATIC_DRAW); 

然後，在繪製函數我做的：

glBindVertexArray(vao); 
    glEnableVertexAttribArray(0); 
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(vertex_data_t), (const GLvoid *)offsetof(vertex_data_t, position)); 
    glEnableVertexAttribArray(1); 
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_TRUE, sizeof(vertex_data_t), (const GLvoid *)offsetof(vertex_data_t, position)); 
    glBindVertexArray(0); 
    glDrawArrays(GL_TRIANGLES, 0, nvertices); 

我越來越漂亮，陰影蘇珊：

http://i.stack.imgur.com/uRjpv.png

但是，這是錯誤的！正常屬性glVertexAttribPointer的最後一個參數應該是12又名（常量GLvoid *）offsetof（vertex_data_t，正常），但是當我這樣做我的蘇珊被打破：

http://i.stack.imgur.com/zBjTS.png

這怎麼可能？着色器如何知道正常的偏移量？

頂點着色器：

 attribute vec3 vertex; 
    attribute vec3 normal; 

    uniform vec4 ambient_color; 
    uniform vec4 diffuse_color; 
    uniform vec3 light_position; 
    uniform mat3 normal_matrix; 
    uniform mat4 model_view_matrix; 
    uniform mat4 model_view_projection_matrix; 

    varying vec4 varying_color; 

    void main(void) { 
       vec4 vertex4 = vec4(vertex.x, vertex.y, vertex.z, 1.0); 
       vec3 eye_normal = normal_matrix * normal; 
       vec4 position4 = model_view_matrix * vertex4; 
       vec3 position3 = position4.xyz/position4.w; 
       vec3 light_direction = normalize(light_position - position3); 
       float diffuse = max(0.0, dot(eye_normal, light_direction)); 
       varying_color.rgb = diffuse * diffuse_color.rgb; 
       varying_color.a = diffuse_color.a; 
       varying_color += ambient_color; 
       gl_Position = model_view_projection_matrix * vertex4; 
    } 

Answer 1

我想你好想是這樣的：

glBindAttribLocation(progId, 0, "vertex"); 
glBindAttribLocation(progId, 1, "normal");