使用OpenGL進行多紋理繪圖？

Question

我正在嘗試使用OpenGL繪制一些具有2個或更多不同紋理的對象。 例如來自3個不同Spritesheets的3個Sprite。 您可以在這里看到我的期望和擁有的東西現在的問題是所有子畫面都來自1個子畫面。 讓我們看一下，首先在初始化時我加載3張圖片img0，img1，img2

img0 = loadSurface2D("image0.png");
img1 = loadSurface2D("image1.png");
img2 = loadSurface2D("image2.png");

然后在我的繪制循環中有點像SDL2：

BKP_Rec dest,src;                                                                                                                    
g2D_renderSurface(img0,NULL,NULL);//will draw all the sprite sheet a (0,0)

src.x = 0;
src.y = 4;
src.w = 64;
src.h = 64;
dest.x = 512;
dest.y = 300;
dest.w = 128;
dest.h = 128;
g2D_renderSurface(img1,&dest,&src);//draw sprite(0,4) 

src.x = 1;
src.y = 2;
dest.x = 562;
dest.y = 300;

g2D_renderSurface(img2,&dest,&src);//draw img 2 sprite(1,2) 

讓我們看看loadSurface2D

Surface2D * loadSurface2D(const char * file)
{
    unsigned  int width, height;
    unsigned char * image = image_loadPNG(file,&width,&height);
    //...all test & flip image are done here, removed it for lisibility
    Surface2D * s = NULL;
    ALLOC_L(Surface2D, s, 1);

    s->data = image;

    s->point[0]  = 0; s->point[1] = 0 ; s->point[2] = 0; s->point[3] = 1;
    s->point[4]  = 0; s->point[5] = -nh; s->point[6] = 0; s->point[7] = 1;
    s->point[8]  = nw; s->point[9] = -nh ; s->point[10] = 0; s->point[11] = 1;
    s->point[12] = nw; s->point[13] = 0 ; s->point[14] = 0; s->point[15] = 1;

    s->texture[0]   = 0.0f; s->texture[1]  = 1.0f ;
    s->texture[2]   = 0.0f; s->texture[3]  = 0.0f;
    s->texture[4]   = 1.0f; s->texture[5]  = 0.0f ;
    s->texture[6]   = 1.0f; s->texture[7]  = 1.0f ;

    s->w = (GLfloat) width;
    s->h = (GLfloat) height;

    bkp_numcal_setIdentity4(s->Mtx_translate);
    bkp_numcal_setIdentity4(s->Mtx_scale);
    bkp_numcal_setIdentity4(s->Mtx_rotate);
    bkp_numcal_setIdentity4(s->Mtx_i);
    bkp_numcal_setIdentity4(s->Mtx);

    GLuint point_vbo = 0;
    glGenBuffers(1,&point_vbo);
    glBindBuffer(GL_ARRAY_BUFFER, point_vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(s->point),s->point,GL_STATIC_DRAW);

    GLuint tex_vbo = 1;
    glGenBuffers(1,&tex_vbo);
    glBindBuffer(GL_ARRAY_BUFFER, tex_vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(s->texture),s->texture,GL_STATIC_DRAW);

    GLuint vao = stc_2d->vao_num;
    stc_2d->vao_num += 1;
    glGenVertexArrays(1,&vao);
    glBindVertexArray(vao);

    glEnableVertexAttribArray(0);
    glBindBuffer(GL_ARRAY_BUFFER, point_vbo);
    glVertexAttribPointer(0,4,GL_FLOAT,GL_FALSE,0,NULL);

    GLuint dimension = 2;
    glEnableVertexAttribArray(1);
    glBindBuffer(GL_ARRAY_BUFFER, tex_vbo);
    glVertexAttribPointer(1,dimension,GL_FLOAT,GL_FALSE,0,NULL);

    s->sampler_loc = glGetUniformLocation(stc_2d->sh_sprite, "basic_texture");
    s->texunit_id = GL_TEXTURE0 + stc_2d->texunit_id;
    stc_2d->texunit_id += 1; // initialized at 0, every function call it increments

    GLuint tex = stc_2d->tex_num;
    ++stc_2d->tex_num;  // same here, another global at 0 when initialized
    glGenTextures(1, &tex);

    glBindTexture(GL_TEXTURE_2D, tex);
    glUseProgram(stc_2d->sprite); // EDITED
    glUniform1i(s->sampler_loc, s->texunit_id);

    glTexImage2D(GL_TEXTURE_2D, 0,
        GL_RGBA, width, height, 0, GL_RGBA,
        GL_UNSIGNED_BYTE, image);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

    int st_offset_loc = glGetUniformLocation(stc_2d->sh_sprite, "vt_");
    glUniformMatrix2fv(st_offset_loc, 1,GL_FALSE, s->vt_);
    s->st_offset = st_offset_loc;

    s->vt_[0] = 0.0;
    s->vt_[1] = 0.0;
    s->vt_[2] = 0.0;
    s->vt_[3] = 0.0;

    s->vao = vao;
    s->texid = tex;
    s->tex_vbo = tex_vbo;
    s->point_vbo = point_vbo;
    return s;
}

基本上我只是加載png創建紋理。 有一些在啟動時初始化為0的值（stc_2D-> *）在計數器ex處起作用：stc_2D-> vba_num告知要創建的當前vba編號。

現在要渲染的功能

void g2D_renderSurface(BKP_Surface2D * s,BKP_Rec * dest,BKP_Rec * src)
{
    glUseProgram(stc_2d->sh_sprite);
    glBindVertexArray(s->vao);

    glActiveTexture(s->texunit_id);
    glBindTexture(GL_TEXTURE_2D, s->texid);
    //glUniform1i(s->sampler_loc, s->texunit_id);

假設我沒有對此行發表評論

    float xf,yf;

    if(dest != NULL)
    {
        xf = (dest->x / (float) stc_fb_width * 2 - 1) ;
        yf = - ((dest->y / (float) stc_fb_height * 2 - 1));
        bkp_numcal_setFreeScalMatrix4(s->Mtx_scale,dest->w /s->w, dest->h/ s->h, 1.0f);
    }
    else
    {
        xf =  - 1 ;
        yf =   1;
        bkp_numcal_setIdentity4(s->Mtx_scale);
    }

    glDrawArrays(GL_TRIANGLE_FAN, 0, 4);

    if(src != NULL)
    {
        s->vt_[0] =(float)(src->x * src->w) / s->w;
        s->vt_[1] = (float) src->w / s->w;
        s->vt_[2] =(s->h - (float)((1 + src->y) * src->h) )/ s->h;
        s->vt_[3] = (float) src->h / s->h;
    }
    else
    {
        s->vt_[0] = 0.0;
        s->vt_[1] = (float) s->w / s->w;
        s->vt_[2] = 0.0;
        s->vt_[3] = (float) s->h / s->h;
    }

    glUniform4fv(s->st_offset,1,s->vt_);

    bkp_numcal_translate4(s->Mtx_translate, xf, yf, 0);
    bkp_numcal_multMat4Mat4(s->Mtx,s->Mtx_scale,s->Mtx_translate);
    glUniformMatrix4fv(stc_2d->mtx_location, 1,GL_FALSE, s->Mtx);
    return;
}

現在結束着色器。

頂點：

#version 410\n
in vec3 vertex_position;uniform mat4 matrix;
in vec2 vt_loc;
varying vec2 v_uv;
uniform vec4 vt_;
void main() 
{
    v_uv.x = (vt_loc.x * vt_[1]) + vt_[0];
    v_uv.y = (vt_loc.y * vt_[3]) + (vt_[2]);

    gl_Position = matrix * vec4(vertex_position, 1.0);
 }

分段：

#version 410
out vec4 frag_colour;
uniform sampler2D basic_texture;
varying vec2 v_uv;
void main() 
{
    vec4 texel = texture(basic_texture, v_uv);
    frag_colour = texel; 
}

我認為它們可能是我不了解的東西，因為我看不到為什么它會繪制3個我想要的大小，我想要的位置但具有唯一紋理的對象。 我以為我會覆蓋相同的紋理，但它是顯示的第一個紋理，而不是最后一個加載的紋理。

Answer 1

glUniform*指定當前程序對象的統一變量的值。
glUseProgram將程序對象安裝為當前渲染狀態的一部分。

將存儲由glUniform*設置的最后一個值。 從loadSurface2D刪除所有統一值設置。 在glUseProgram(stc_2d->sh_sprite);之后glUseProgram(stc_2d->sh_sprite);在g2D_renderSurface進行統一值的所有設置glUseProgram(stc_2d->sh_sprite); 。

還要注意，您必須分配給紋理采樣器統一basic_texture值不是紋理單元枚舉常量 （ 不是GL_TEXTURE0 ， GL_TEXTURE1 ，... ）。
它必須是紋理單位的編號（0，1，2. ...） 。

這是錯誤的：

s->texunit_id = GL_TEXTURE0 + stc_2d->texunit_id;
glUniform1i(s->sampler_loc, s->texunit_id);

它一定要是：

s->texunit_id = stc_2d->texunit_id;

.....

glUseProgram(stc_2d->sh_sprite);

glActiveTexture(s->texunit_id + GL_TEXTURE0); // GL_TEXTURE0, GL_TEXTURE1, GL_TEXTURE2, ....
glBindTexture(GL_TEXTURE_2D, s->texid);
glUniform1i(s->sampler_loc, s->texunit_id);   // 0, 1, 2, ....

Answer 2

着色器中的均勻度始終存儲它們設置為的最后狀態。 由於在繪制之前更改了活動紋理，因此還必須更新采樣器制服（該行已經存在，不確定為什么要添加注釋）。

glActiveTexture(s->texunit_id);
glBindTexture(GL_TEXTURE_2D, s->texid);
glUniform1i(s->sampler_loc, s->texunit_id); //<-- This is important