c++ - glDrawElements 抛出 GL_INVALID_VALUE 错误

Question

我正在尝试绘制部分平铺图像，但在调用 glDrawElements 函数时出现 GL_INVALID_VALUE 错误。当我用 glDrawArrays 更改此功能时没有问题。问题是索引计数参数不是负数。

有一个代码:

#define BUFFER_OFFSET(i) ((char *)nullptr + (i))
 #define VERTEX_ATTR_PTR(loc, count, member, type) \
    glEnableVertexAttribArray(loc); \
    glVertexAttribPointer(loc, count, GL_FLOAT, GL_FALSE, sizeof(type),  BUFFER_OFFSET(offsetof(struct type, member)))
// ---------- TextRenderer
void TextRenderer::setText(const string& text) {
    vector<Vertex2f> vertex_buffer;
    vector<GLuint> index_buffer;

    GLfloat cursor = 0.f;
    FPoint2D cell_size = font->getCellSize();

    for (char c : text) {
        TILE_ITER iter = font->getCharacter(c);
        {
            // UV
            for (GLuint i = 0; i < 4; ++i) {
                TILE_ITER _v = iter + i;
                vertex_buffer.push_back( {
                        {
                                _v->pos[0]  + cursor,
                                _v->pos[1],
                                _v->pos[2]
                        },
                        { _v->uv[0], _v->uv[1] }
                });
            }
            // Index
            for (GLuint i = 0; i < 6; ++i)
                index_buffer.push_back(
                        Tile::indices[i] + vertex_buffer.size() - 4);
        }
        cursor += cell_size.X;
    }

    vertices_count = vertex_buffer.size();
    indices_count = index_buffer.size();

    glBindVertexArray(vao);
    {
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indices);
        glBufferSubData(GL_ELEMENT_ARRAY_BUFFER,
                0,
                indices_count * sizeof(GLuint),
                &index_buffer[0]);
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);

        glBindBuffer(GL_ARRAY_BUFFER, vbo);
        glBufferSubData(GL_ARRAY_BUFFER,
                0,
                vertices_count * sizeof(Vertex2f),
                &vertex_buffer[0]);
        glBindBuffer(GL_ARRAY_BUFFER, 0);
    }
    glBindVertexArray(0);
}
void TextRenderer::create() {
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);
    {
        indices = genGLBuffer( {
                nullptr,
                BUFFER_SIZE / 2 * sizeof(GLuint),
                GL_ELEMENT_ARRAY_BUFFER
        }, true, GL_DYNAMIC_DRAW);

        vbo = genGLBuffer( {
                nullptr,
                BUFFER_SIZE * sizeof(Vertex2f),
                GL_ARRAY_BUFFER
        }, true, GL_DYNAMIC_DRAW);

        VERTEX_ATTR_PTR(0, 3, pos, Vertex2f); // Vertex
        VERTEX_ATTR_PTR(1, 2, uv, Vertex2f); // UV
    }
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
    glBindVertexArray(0);

    setText("DUPA");
}
void TextRenderer::draw(MatrixStack& matrix, GLint) {
    static Shader shader(
            getFileContents("shaders/text_frag.glsl"),
            getFileContents("shaders/text_vert.glsl"),
            "");

    shader.begin();
    shader.setUniform(GL_TEXTURE_2D, "texture", 0,
            font->getHandle());
    shader.setUniform("matrix.mvp", matrix.vp_matrix * matrix.model);
    shader.setUniform("col", col);
    {
        glBindVertexArray(vao);
        //glDrawArrays(GL_LINE_STRIP, 0, vertices_count);
        glDrawElements(GL_LINES, indices_count, GL_UNSIGNED_INT,
                nullptr);
        glBindVertexArray(0);
        showGLErrors();
    }
    shader.end();
}

Answer 1

问题出在您的 setText() 方法中的以下(缩短的)调用序列:

glBindVertexArray(vao);
{
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indices);
    glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, ...);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);

    ...
}
glBindVertexArray(0);

GL_ELEMENT_ARRAY_BUFFER 的绑定(bind)是 VAO 状态的一部分。因此，通过在绑定(bind) VAO 时进行此调用:

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);

您正在将 VAO 状态设置为具有 0 的元素数组缓冲区绑定(bind)。因此，当您稍后在 draw() 方法中绑定(bind) VAO 时，您将不会绑定(bind) GL_ELEMENT_ARRAY_BUFFER。

为避免这种情况，最简单的解决方案是删除该调用。如果因为担心绑定(bind)它可能会对其他代码产生不良副作用而想显式取消绑定(bind)，则需要在取消绑定(bind) VAO 后移动它:

glBindVertexArray(vao);
{
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indices);
    glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, ...);

    ...
}
glBindVertexArray(0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);