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glDrawarrays drawing from the wrong vertexbuffer
1 month ago Edited by C_Worm on May 10, 2021, 2:48 p.m.
Hi!

Im trying to use two VBO's, one for sprites and one for font/text rendering.

However the glDrawArrays() inside CreateText() function doesn't draw the vertices produced and sent with glBufferSubData to the vbo_text buffer.

I've been thinking that the problem is that InitializeVBO() is setting the glEnableVerteArray() to the same positions as the vbo_sprite.

But can't you let the attribindex be the same for different VBO's?

I mean, shouldn't this work?

gen/bind buffer 1

glEnableVertexAttrib(0); glVertexAttriPointer(0, ... ..., pos);
glEnableVertexAttrib(1); glVertexAttriPointer(1, ... ..., col);
glEnableVertexAttrib(2); glVertexAttriPointer(2, ... ..., texCoord);

gen/bind buffer 2

glEnableVertexAttrib(0); glVertexAttriPointer(0, ... ..., pos);
glEnableVertexAttrib(1); glVertexAttriPointer(1, ... ..., col);
glEnableVertexAttrib(2); glVertexAttriPointer(2, ... ..., texCoord);


or must you do this?


gen/bind buffer 1

glEnableVertexAttrib(0); glVertexAttriPointer(0, ... ..., pos);
glEnableVertexAttrib(1); glVertexAttriPointer(1, ... ..., col);
glEnableVertexAttrib(2); glVertexAttriPointer(2, ... ..., texCoord);

gen/bind buffer 2

glEnableVertexAttrib(3); glVertexAttriPointer(3, ... ..., pos);
glEnableVertexAttrib(4); glVertexAttriPointer(4, ... ..., col);
glEnableVertexAttrib(5); glVertexAttriPointer(5, ... ..., texCoord);

----------------------------------------------------------------------


aaand.... i know the CreateText isn't very efficient but i just want it to be simple and easy to get some text to the screen.

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bool running = true;

#include "assert.h"
#include "cj_engine.h"

GLenum err = 0;


bool init = false;

struct RENDERER
{
	u32 VAO;

};

struct CJ_VTX_QUAD
{
	V2f pos;
	V4f col;
	V2f tCoord;
};

struct TILEMAP
{
	u32 w;
	u32 h;
	ENTITY *entity;
};

struct GAME_HANDLER
{
	ENTITY entity_batch[1000];
	u32 entity_used;
	u32 entity_id;

	CJ_VTX_QUAD *pVertex;
	u32 vtx_id;

	TILEMAP tilemap;

	ENTITY *player;
	ENTITY *monster;

	ENTITY *camera;


};

struct CJ_VBO
{
	u32 id;
	u8 *base;
	u32 used;
	u32 size;

};


RENDERER CreateRenderer()
{

	RENDERER renderer = {};

	glGenVertexArrays(1, &renderer.VAO);
	glBindVertexArray(renderer.VAO);

	glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
	glEnable(GL_BLEND);
	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

	return renderer;
}


struct CJ_VTX_ATTRIB
{
	u32 size;
	GLenum type;
	u32 stride;
	u32 offset;
};

u32 CreateText(CJ_PLATFORM *platform, CJ_VBO *vbo, TEXTUREINFO tex_i, char *str, V2f pos, V4f col);

void InitializeVBO(CJ_VBO *vbo, u8* base, u32 size, u32 n_attribs, CJ_VTX_ATTRIB *vtx_attrib)
{
	vbo->base = base;
	vbo->size = size;

	glGenBuffers(1, &vbo->id);
	glBindBuffer(GL_ARRAY_BUFFER, vbo->id);
	glBufferData(GL_ARRAY_BUFFER, vbo->size, vbo->base, GL_DYNAMIC_DRAW);

	for(u32 i = 0; i < n_attribs; i++)
	{
		vtx_attrib[i].offset *= sizeof(float);
		vtx_attrib[i].stride *= sizeof(float);
		glEnableVertexAttribArray(i);	glVertexAttribPointer(i, vtx_attrib[i].size, vtx_attrib[i].type, false, vtx_attrib[i].stride, (void*)vtx_attrib[i].offset);
	}


}



void InitQuad(CJ_VBO *vbo, u32 index, V2f pos, V2f size)
{
	CJ_VTX_QUAD *vertex = (CJ_VTX_QUAD*)vbo->base;
	vertex[index + 0].pos = v2f(pos.x, pos.y);
	vertex[index + 1].pos = v2f(pos.x, pos.y + size.y);
	vertex[index + 2].pos = v2f(pos.x + size.x, pos.y + size.y);
	vertex[index + 3].pos = v2f(pos.x + size.x, pos.y);
}

void SetQuad_X(CJ_VBO *vbo, u32 index, float x)
{
	CJ_VTX_QUAD *vertex = (CJ_VTX_QUAD*)vbo->base;
	vertex[index + 0].pos.x = x;
	vertex[index + 1].pos.x = x;
}

void SetQuad_Y(CJ_VBO *vbo, u32 index, float y)
{
	CJ_VTX_QUAD *vertex = (CJ_VTX_QUAD*)vbo->base;
	vertex[index + 0].pos.y = y;
	vertex[index + 1].pos.y = y;
}

void SetQuad_W(CJ_VBO *vbo, u32 index, float w)
{
	CJ_VTX_QUAD *vertex = (CJ_VTX_QUAD*)vbo->base;
	vertex[index + 2].pos.x = vertex[index + 0].pos.x + w;
	vertex[index + 3].pos.x = vertex[index + 0].pos.x + w;
}


void SetQuad_H(CJ_VBO *vbo, u32 index, float h)
{
	CJ_VTX_QUAD *vertex = (CJ_VTX_QUAD*)vbo->base;
	vertex[index + 2].pos.y = vertex[index + 0].pos.y + h;
	vertex[index + 3].pos.y = vertex[index + 0].pos.y + h;
}

void SetQuad_Col(CJ_VBO *vbo, u32 index, V4f col)
{
	CJ_VTX_QUAD *vertex = (CJ_VTX_QUAD*)vbo->base;
	vertex[index + 0].col = col;
	vertex[index + 1].col = col;
	vertex[index + 2].col = col;
	vertex[index + 3].col = col;
}

ENTITY *PushEntity(GAME_HANDLER *game, u32 size)
{
	assert(game->entity_used + size <= ArrayCount(game->entity_batch));

	ENTITY *entity 		= 0;
	CJ_VTX_QUAD *vtx	= 0;

	entity			= game->entity_batch + game->entity_used;;
	entity->id 		= game->entity_id;

	vtx			= game->pVertex + game->vtx_id;

	game->vtx_id		+= 4 * size;
	game->entity_used += size;
	game->entity_id++;
	

	return entity;
}

void UpdateVBO_Entity(CJ_VBO *vbo, GAME_HANDLER *game)
{
	CJ_VTX_QUAD *pVertex = (CJ_VTX_QUAD*)vbo->base;

	assert(game->entity_used <= ArrayCount(game->entity_batch));

	for(u32 i = 0; i < game->entity_used; i++)
	{
		V2f pos 	= game->entity_batch[i].pos;
		V2f size 	= game->entity_batch[i].size;
		V4f col 	= game->entity_batch[i].col;
		V2f tCoord_p	= game->entity_batch[i].texcoord_pos;
		V2f tCoord_sz	= game->entity_batch[i].texcoord_size;

		pVertex[(i * 4) + 0].pos = v2f(pos.x, pos.y);
		pVertex[(i * 4) + 1].pos = v2f(pos.x, pos.y + size.y);
		pVertex[(i * 4) + 2].pos = v2f(pos.x + size.x, pos.y + size.y);
		pVertex[(i * 4) + 3].pos = v2f(pos.x + size.y, pos.y);

		pVertex[(i * 4) + 0].col = col;
		pVertex[(i * 4) + 1].col = col;
		pVertex[(i * 4) + 2].col = col;
		pVertex[(i * 4) + 3].col = col;

		pVertex[(i * 4) + 0].tCoord = v2f(tCoord_p.x, tCoord_p.y);
		pVertex[(i * 4) + 1].tCoord = v2f(tCoord_p.x, tCoord_p.y + tCoord_sz.y);
		pVertex[(i * 4) + 2].tCoord = v2f(tCoord_p.x + tCoord_sz.x, tCoord_p.y + tCoord_sz.y);
		pVertex[(i * 4) + 3].tCoord = v2f(tCoord_p.x + tCoord_sz.y, tCoord_p.y);

	}

}
void OnGameInit(CJ_PLATFORM *platform, GAME_HANDLER *game)
{
	if(!init)
	{

		u32 tilemap_w = 2;
		u32 tilemap_h = 2;
		V2f start_pos = v2f(1.0f, 0.0f);
		V2f tile_size = v2f(0.11f, 0.11f);
		game->tilemap.entity = PushEntity(game, tilemap_w * tilemap_h);
		game->tilemap.w = tilemap_w;
		game->tilemap.h = tilemap_h;
	

		for(u32 y = 0; y < tilemap_h; y++)
		{
			for(u32 x = 0; x < tilemap_w; x++)
			{
				u32 index = x + (y * tilemap_w);

				V2f pos = v2f(start_pos.x + (x * tile_size.x), start_pos.y + (y * tile_size.y));
				V2f size = v2f(tile_size.x - 0.01f, tile_size.y - 0.01f);
				V4f col = v4f(1.0f, 1.0f, 1.0f, 0.2f);

				game->tilemap.entity[index].pos = pos;
				game->tilemap.entity[index].size = size;
				game->tilemap.entity[index].col = col;
				game->tilemap.entity[index].texcoord_pos = v2f(0.0f, 0.0f);
				game->tilemap.entity[index].texcoord_size = v2f(1.0f, 1.0f);


			}

		}

		game->player = PushEntity(game, 1);
		game->player->pos = v2f(0.0f, 0.0f); 
		game->player->size = v2f(0.3f, 0.3f); 
		game->player->col = v4f(1.0f, 1.0f, 0.0f, 0.2f); 
		game->player->texcoord_pos = v2f(0.0f, 0.0f);
		game->player->texcoord_size = v2f(1.0f, 1.0f);

		game->monster = PushEntity(game, 1);
		game->monster->pos = v2f(1.0f, 1.0f); 
		game->monster->size = v2f(0.2f, 0.2f); 
		game->monster->texcoord_pos = v2f(0.0f, 0.0f);
		game->monster->texcoord_size = v2f(1.0f, 1.0f);
		game->monster->col = v4f(1.0f, 1.0f, 0.0f, 0.2f); 

		game->camera = PushEntity(game, 1);
		game->camera->pos = v2f(0.0f, 0.0f);




		init = true;
	}

}

void OnGameUpdate(CJ_PLATFORM *platform, GAME_HANDLER *game)
{
	if(glfwGetKey(platform->window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
	{
		running = false;
	}

	float mov = 0.02f;

	game->camera->vel = v2f(0.f, 0.f);
	if(glfwGetKey(platform->window, GLFW_KEY_UP) == GLFW_PRESS)
	{
		game->camera->vel.y = mov;
	}
	if(glfwGetKey(platform->window, GLFW_KEY_DOWN) == GLFW_PRESS)
	{
		game->camera->vel.y = -mov;
	}
	if(glfwGetKey(platform->window, GLFW_KEY_RIGHT) == GLFW_PRESS)
	{
		game->camera->vel.x = mov;
	}
	if(glfwGetKey(platform->window, GLFW_KEY_LEFT) == GLFW_PRESS)
	{
		game->camera->vel.x = -mov;
	}


	game->player->pos += game->camera->vel;
	bool clamped = false;
	if(game->player->pos.x < game->player->size.x)
	{
		clamped = true;
		game->player->pos.x = game->player->size.x;
	}

	if(game->player->pos.x + game->player->size.x > 2.0f - game->player->size.x)
	{
		clamped = true;
		game->player->pos.x = 2.0f - (2.0f*game->player->size.x);

	}
	if(game->player->pos.y < game->player->size.y)
	{
		clamped = true;
		game->player->pos.y = game->player->size.y;
	}

	if(game->player->pos.y + game->player->size.y > 2.0f - game->player->size.y)
	{
		clamped = true;
		game->player->pos.y = 2.0f - (2.0f*game->player->size.y);

	}

	if(clamped)
	{
		for(u32 i = game->tilemap.entity->id; i < game->tilemap.w  * game->tilemap.h; i++)
		{
			game->entity_batch[i].pos -= game->camera->vel;
		}
	}

}


int main()
{

	CJ_PLATFORM platform = CreatePlatform(640, 480, "Platform", 0);
	RENDERER renderer = CreateRenderer();


	SHADER_PROGRAM shader_solid_col = {}; 
	CreateShader(&shader_solid_col, "..\\shader\\VS.h", GL_VERTEX_SHADER);
	CreateShader(&shader_solid_col, "..\\shader\\FS_solid_col.h", GL_FRAGMENT_SHADER);
	LinkShaderProgram(&shader_solid_col);
	UseShaderProgram(&shader_solid_col);

	SHADER_PROGRAM shader_textured = {}; 
	CreateShader(&shader_textured, "..\\shader\\VS.h", GL_VERTEX_SHADER);
	CreateShader(&shader_textured, "..\\shader\\FS_Texture.h", GL_FRAGMENT_SHADER);
	LinkShaderProgram(&shader_textured);
	UseShaderProgram(&shader_textured);

	SHADER_PROGRAM shader_font = {}; 
	CreateShader(&shader_font, "..\\shader\\VS.h", GL_VERTEX_SHADER);
	CreateShader(&shader_font, "..\\shader\\FS_Texture.h", GL_FRAGMENT_SHADER);
	LinkShaderProgram(&shader_font);
	UseShaderProgram(&shader_font);

	CJ_VTX_ATTRIB vbo_text_attrib[3];
	vbo_text_attrib[0].size = 2;
	vbo_text_attrib[0].type = GL_FLOAT;
	vbo_text_attrib[0].stride = 8;
	vbo_text_attrib[0].offset = 0;

	vbo_text_attrib[1].size = 4;
	vbo_text_attrib[1].type = GL_FLOAT;
	vbo_text_attrib[1].stride = 8;
	vbo_text_attrib[1].offset = 2;

	vbo_text_attrib[2].size = 2;
	vbo_text_attrib[2].type = GL_FLOAT;
	vbo_text_attrib[2].stride = 8;
	vbo_text_attrib[2].offset = 6;

	u8 *vertex_memory_for_text = (u8*)calloc(4 * 6, sizeof(float));
	CJ_VBO vbo_text = {};
	InitializeVBO(&vbo_text, vertex_memory_for_text, 4*6*sizeof(float), ArrayCount(vbo_text_attrib), vbo_text_attrib);


	CJ_VTX_ATTRIB vbo_sprite_attrib[3];
	vbo_sprite_attrib[0].size = 2;
	vbo_sprite_attrib[0].type = GL_FLOAT;
	vbo_sprite_attrib[0].stride = 8;
	vbo_sprite_attrib[0].offset = 0;

	vbo_sprite_attrib[1].size = 4;
	vbo_sprite_attrib[1].type = GL_FLOAT;
	vbo_sprite_attrib[1].stride = 8;
	vbo_sprite_attrib[1].offset = 2;

	vbo_sprite_attrib[2].size = 2;
	vbo_sprite_attrib[2].type = GL_FLOAT;
	vbo_sprite_attrib[2].stride = 8;
	vbo_sprite_attrib[2].offset = 6;

	u8 *vertex_memory = (u8*)calloc(4 * 32 * 1000, sizeof(float));
	const u32 size = 4 * 32 * 1000 * sizeof(float);
	CJ_VBO vbo_sprite = {};
	InitializeVBO(&vbo_sprite, vertex_memory, size, ArrayCount(vbo_sprite_attrib), vbo_sprite_attrib);

	u32 IBO = 0;
	const u32 quads = size / (sizeof(CJ_VTX_QUAD) * 4);
	u32 ibo_data[quads * 6] = {};
	for(u32 i = 0; i < quads; i++)
	{
		ibo_data[0 + (i * 6)] = 0 + (i * 4);
		ibo_data[1 + (i * 6)] = 1 + (i * 4);
		ibo_data[2 + (i * 6)] = 2 + (i * 4);
		ibo_data[3 + (i * 6)] = 0 + (i * 4);
		ibo_data[4 + (i * 6)] = 2 + (i * 4);
		ibo_data[5 + (i * 6)] = 3 + (i * 4);
	}

	glGenBuffers(1, &IBO);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, IBO);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(ibo_data), ibo_data, GL_DYNAMIC_DRAW);



	GAME_HANDLER game = {};
	game.pVertex = (CJ_VTX_QUAD*)vbo_sprite.base;
	TEXTUREINFO texture_batch[10] = {};
	LoadTexture(&texture_batch[0], "assets\\tileSheet32x32.png", LOAD_IMAGE, 0);
	LoadTexture(&texture_batch[1], "C:\\windows\\fonts\\cour.ttf", LOAD_FONT, 48);


	while(!glfwWindowShouldClose(platform.window) && running)
	{

		glfwPollEvents();

		glfwGetWindowSize(platform.window, &platform.win_w, &platform.win_h);
		glViewport(0, 0, platform.win_w, platform.win_h);
		glClearColor(0.2f, 0.1f, 0.1f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT);

		OnGameInit(&platform, &game);
		OnGameUpdate(&platform, &game);
		

		glBindBuffer(GL_ARRAY_BUFFER, vbo_sprite.id);
		UpdateVBO_Entity(&vbo_sprite, &game);
		glBufferSubData(GL_ARRAY_BUFFER, 0, vbo_sprite.size, (void*)vbo_sprite.base);

		UseShaderProgram(&shader_textured);
		glBindTexture(GL_TEXTURE_2D, texture_batch[0].texture_id);
		glDrawElements(GL_TRIANGLES, 6 * 1000, GL_UNSIGNED_INT, (const void*)0); 

		UseShaderProgram(&shader_solid_col);
		CreateText(&platform, &vbo_text, texture_batch[1], "12345", v2f(1.0f, 1.0f), v4f(1.0f, 1.0f, 1.0f, 1.0f));



		SwapBuffers(platform);
	}



	glfwTerminate();
    
    
    return 0;
}

u32 CreateText(CJ_PLATFORM *platform, CJ_VBO *vbo, TEXTUREINFO tex_i, char *str, V2f pos, V4f col)
{
	char line[1024] = {};
	strcpy(line, str);
	
	// xp & yp is baseline in stbtt_GetPackedQuad();
	float yp = 0.0f;
	float xp = 0.0f;
	
	float t_pos_x = 0.0f;
	float t_pos_y = 0.0f;
	float t_sz_x = 0.0f;
	float t_sz_y = 0.0f;
	
	float c_x = 0.0f;
	float c_y = 0.0f;
	
	float c_w = 0.0f;
	float c_h = 0.0f;
	
	glBindBuffer(GL_ARRAY_BUFFER, vbo->id);
	glBindTexture(GL_TEXTURE_2D, tex_i.texture_id);
	
	u32 last_quad_index = 0;
	u32 last_text_q = 0;
	u32 n_quads_written = 0;

	float *pVertex = (float*)vbo->base;
	
	for(i32 i = 0; i < strlen(line); i++)
	{
	    stbtt_GetPackedQuad(tex_i.packed_char, 1024, 1024, line[i] - ' ', &xp, &yp, &tex_i.glyph_quad, 0);
	    
	    t_pos_x = tex_i.glyph_quad.s0;
	    t_pos_y = 1.0f - tex_i.glyph_quad.t1;
	    t_sz_x = tex_i.glyph_quad.s1 - tex_i.glyph_quad.s0;
	    t_sz_y = (1.0f - tex_i.glyph_quad.t0) - (1.0f - tex_i.glyph_quad.t1);
	    
	    // The glyph_quad.x0 & glyph_quad.y0 should be the the advancing positions in x/y, yp is the baseline which has to used when calculating the char y_pos 
	    c_x = pos.x + (tex_i.glyph_quad.x0)  / platform->win_w;
	    c_y = pos.y + ((yp + (yp - tex_i.glyph_quad.y1))) / platform->win_h;
	    
	    c_w = (tex_i.glyph_quad.x1 - tex_i.glyph_quad.x0)  / platform->win_w;
	    c_h = (tex_i.glyph_quad.y1 - tex_i.glyph_quad.y0)  / platform->win_h;
	
	    pVertex[0] = c_x; 		pVertex[1] = c_y;		pVertex[2]  = t_pos_x;		pVertex[3]  = t_pos_y;
	    pVertex[4] = c_x; 		pVertex[5] = c_y + c_h;		pVertex[6]  = t_pos_x;		pVertex[7]  = t_pos_y + t_sz_y;
	    pVertex[8] = c_x + c_w; 	pVertex[9] = c_y + c_h;		pVertex[10] = t_pos_x + t_sz_x;	pVertex[11] = t_pos_y + t_sz_y;

	    pVertex[12] = c_x; 		pVertex[13] = c_y;		pVertex[14] = t_pos_x;		pVertex[15] = t_pos_y;
	    pVertex[16] = c_x + c_w;	pVertex[17] = c_y + c_h;	pVertex[18] = t_pos_y + t_sz_x;	pVertex[19] = t_pos_y + t_sz_y;
	    pVertex[20] = c_x + c_w;	pVertex[21] = c_y;		pVertex[22] = t_pos_y + t_sz_x;	pVertex[23] = t_pos_y;
	    
	    //float vertices[6][4] = 
	    //{
	    //	c_x, c_y,	 	t_pos_x, t_pos_y,
	    //	c_x, c_y + c_h, 	t_pos_x, t_pos_y + t_sz_y,
	    //	c_x + c_w, c_y + c_h,	t_pos_x + t_sz_x, t_pos_y + t_sz_y,
	
	    //	c_x, c_y,		t_pos_x, t_pos_y,
	    //	c_x + c_w, c_y + c_h,	t_pos_x + t_sz_x, t_pos_y + t_sz_y,
	    //	c_x + c_w, c_y,		t_pos_x +t_sz_x, t_pos_y
	    //};
	
	    glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vbo->base), vbo->base);
	    glDrawArrays(GL_TRIANGLES, 0, 6);
	
	
	    
	}
	
	//return last_quad_index;
	return last_text_q;
} 
Simon Anciaux
1004 posts
glDrawarrays drawing from the wrong vertexbuffer
1 month ago
I'm rusty about all the OpenGL setup, but here are some things you may want to check:

- The values for stride and offset you pass to glVertexAttribPointer need to be in bytes. Unless I'm mistaken about your code, you need to multiply them by 4 ( sizeof( float ) );
- You may need to query the vertex attrib index values from your shaders, unless the shaders use layout(location = x);
- Your text VBO is setup for color information but the CreateText function doesn't send color information;
- glBufferSubData in CreateText uses sizeof( vbo->base ) as the size which is the size of a pointer ( 8 ), but it should be 6 * ( 2 + 2 ) * 4: 6 vertices * ( positions + uvs ) * sizeof( float ).
- It would most likely be better to call glBufferSubData several time with a single draw call instead of a draw call per character. Even better (I guess) would be to do 1 glBufferSubData and 1 draw call for all the text.
97 posts
glDrawarrays drawing from the wrong vertexbuffer
1 month ago
Allright big thanks!

I also found a small bug in the naming of variables in the shader, but now it works.